DOC: fix numpydoc section titles in misc plotting docstrings
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19899?src=pr&el=h1) Report
> Merging [#19899](https://codecov.io/gh/pandas-dev/pandas/pull/19899?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8f1dfa74e244622a7f356a496072f93dce032839?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19899/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/19899?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19899      +/-   ##
==========================================
- Coverage   91.67%   91.66%   -0.01%     
==========================================
  Files         150      150              
  Lines       48936    48938       +2     
==========================================
  Hits        44860    44860              
- Misses       4076     4078       +2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.04% <ø> (-0.01%)` | :arrow_down: |
| #single | `41.81% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19899?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_misc.py](https://codecov.io/gh/pandas-dev/pandas/pull/19899/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19taXNjLnB5) | `38.98% <ø> (ø)` | :arrow_up: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/19899/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `87.68% <0%> (-0.3%)` | :arrow_down: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
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