CLN: replace %s syntax with .format in stats/moments.py
- [x] Progress towards #16130
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

sorry, should have said something. This file is about to be removed (as its entirely deprecated). so no need to change. cc @topper-123  # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18650?src=pr&el=h1) Report
> Merging [#18650](https://codecov.io/gh/pandas-dev/pandas/pull/18650?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/6b6cfb84ed37c94cbae54e89437c14fe84cbdc4f?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18650/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18650?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18650      +/-   ##
==========================================
- Coverage    91.6%   91.57%   -0.03%     
==========================================
  Files         153      153              
  Lines       51250    51210      -40     
==========================================
- Hits        46947    46897      -50     
- Misses       4303     4313      +10
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.43% <100%> (-0.02%)` | :arrow_down: |
| #single | `40.66% <100%> (-0.13%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18650?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/stats/moments.py](https://codecov.io/gh/pandas-dev/pandas/pull/18650/diff?src=pr&el=tree#diff-cGFuZGFzL3N0YXRzL21vbWVudHMucHk=) | `68.96% <100%> (-2.24%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18650/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18650/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.81% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/window.py](https://codecov.io/gh/pandas-dev/pandas/pull/18650/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvd2luZG93LnB5) | `96.31% <0%> (-0.07%)` | :arrow_down: |
| [pandas/tseries/offsets.py](https://codecov.io/gh/pandas-dev/pandas/pull/18650/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvb2Zmc2V0cy5weQ==) | `96.86% <0%> (-0.04%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18650?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/18650?src=pr&el=footer). Last update [6b6cfb8...02e7dcc](https://codecov.io/gh/pandas-dev/pandas/pull/18650?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Yes this module has been deprecated and I will do a PR this week or weekend removing this. 

There are plenty of other places where similar PRs to this can be done, so you’re very welcome to do similar PRs to this on other files:-)