DOC: Fix flake 8 errors for whatsnew v0.16*
- [x] closes #24237
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=h1) Report
> Merging [#24338](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/380eaf1494eaa0e37dc6d6019bf03d1e92f34e9a?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24338/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24338      +/-   ##
==========================================
+ Coverage   92.28%   92.28%   +<.01%     
==========================================
  Files         162      162              
  Lines       51835    51835              
==========================================
+ Hits        47834    47835       +1     
+ Misses       4001     4000       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <ø> (ø)` | :arrow_up: |
| #single | `43% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24338/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `87.58% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24338?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/24338?src=pr&el=footer). Last update [380eaf1...ef6cf0e](https://codecov.io/gh/pandas-dev/pandas/pull/24338?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/24338?src=pr&el=h1) Report
> Merging [#24338](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/380eaf1494eaa0e37dc6d6019bf03d1e92f34e9a?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24338/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24338      +/-   ##
==========================================
+ Coverage   92.28%   92.28%   +<.01%     
==========================================
  Files         162      162              
  Lines       51835    51835              
==========================================
+ Hits        47834    47835       +1     
+ Misses       4001     4000       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <ø> (ø)` | :arrow_up: |
| #single | `43% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24338/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `87.58% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24338?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/24338?src=pr&el=footer). Last update [380eaf1...ef6cf0e](https://codecov.io/gh/pandas-dev/pandas/pull/24338?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!