DOC: fix DataFrame.quantile docstring and doctests
- [x] closes #22898
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Based on #22459. Fix the docstring for DataFrame.quantile. I also updated `ci/code_checks.sh`.
Hello @Moisan! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/frame.py`](https://github.com/Moisan/pandas/blob/0f6592fafadaf60f06c3c7509a6bc02050d5006a/pandas/core/frame.py) !

 Crap forgot to double check the open pull requests before working on this. Closing in favor of #22906. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23936?src=pr&el=h1) Report
> Merging [#23936](https://codecov.io/gh/pandas-dev/pandas/pull/23936?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c0b9eea7067d6089fabdc31ac2ed4cc16d063568?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23936/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23936?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23936   +/-   ##
=======================================
  Coverage    92.2%    92.2%           
=======================================
  Files         162      162           
  Lines       51700    51700           
=======================================
  Hits        47669    47669           
  Misses       4031     4031
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.6% <ø> (ø)` | :arrow_up: |
| #single | `43.02% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23936?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/23936/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.91% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23936?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/23936?src=pr&el=footer). Last update [c0b9eea...2c972ba](https://codecov.io/gh/pandas-dev/pandas/pull/23936?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @Moisan, #22906 is stale. Reopening this. If you don't mind taking a look at the discussions there, and finish the changes here, that would be great. @Moisan can you merge master and push again. CI is fixed now. thanks @Moisan 