CLN: Replacing %s with .format in pandas/core/frame.py
- [x] Progress towards #16130
- [x] tests added / passed
- [x] passes git diff upstream/master -u -- "*.py" | flake8 --diff
looks good. circle ci seems to be failing. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20461?src=pr&el=h1) Report
> Merging [#20461](https://codecov.io/gh/pandas-dev/pandas/pull/20461?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/4a344972722cc3c27250cbc8e382472b13e66bde?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `88.23%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20461/graphs/tree.svg?height=150&src=pr&token=eZ4WkYLtcO&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/20461?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #20461   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
=======================================
  Files         153      153           
  Lines       49295    49295           
=======================================
  Hits        45274    45274           
  Misses       4021     4021
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <88.23%> (ø)` | :arrow_up: |
| #single | `41.89% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20461?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/20461/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.16% <88.23%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20461?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/20461?src=pr&el=footer). Last update [4a34497...9931432](https://codecov.io/gh/pandas-dev/pandas/pull/20461?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Merged in master and pushed. @AaronCritchley let us know if you notice that the CI all passes. thanks!