CLN: replace %s syntax with .format in io/formats/format.py
Progress toward issue #16130. Converted old string formatting to new string formatting in io/formats/format.py.

- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`


I believe this failing test is addressed in this PR:
https://github.com/pandas-dev/pandas/pull/17355 > I believe this failing test is addressed in this PR:

@cbertinato : Yes, you are correct.  Please ignore this failure for your PR. @cbertinato : This PR looks good to go, but I think we'll hold on merging until we fix the test failure. Sounds good. Awesome.  Thanks for understanding.

We'll ping when it's merged so you can rebase and get all tests to pass. if you can rebase and push again # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=h1) Report
> Merging [#17358](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e8a1765edf91ec4d087b46b90d5e54530550029b?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `89.09%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17358/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17358      +/-   ##
==========================================
+ Coverage   91.01%   91.02%   +<.01%     
==========================================
  Files         163      162       -1     
  Lines       49561    49570       +9     
==========================================
+ Hits        45107    45119      +12     
+ Misses       4454     4451       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.8% <89.09%> (+0.02%)` | :arrow_up: |
| #single | `40.24% <23.63%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.05% <89.09%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.72% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `95.87% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.99% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/accessor.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYWNjZXNzb3IucHk=) | | |
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.48% <0%> (+0.02%)` | :arrow_up: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `95% <0%> (+0.04%)` | :arrow_up: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `96.02% <0%> (+0.06%)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.05% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=footer). Last update [e8a1765...01f796e](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=h1) Report
> Merging [#17358](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/0d676a3ccf1d7aa986416a7488b941496f936d98?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `89.09%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17358/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17358      +/-   ##
==========================================
+ Coverage   91.01%   91.02%   +<.01%     
==========================================
  Files         163      163              
  Lines       49567    49570       +3     
==========================================
+ Hits        45113    45119       +6     
+ Misses       4454     4451       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.8% <89.09%> (+0.02%)` | :arrow_up: |
| #single | `40.26% <23.63%> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.05% <89.09%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.72% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.05% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=footer). Last update [0d676a3...f18636a](https://codecov.io/gh/pandas-dev/pandas/pull/17358?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!