DOC: fix various warnings and errors in the docs (from deprecations/api changes
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19763?src=pr&el=h1) Report
> Merging [#19763](https://codecov.io/gh/pandas-dev/pandas/pull/19763?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9df5ab781f903ce00407630aa9db661e3f739bcf?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/19763/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/19763?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #19763   +/-   ##
=======================================
  Coverage    91.6%    91.6%           
=======================================
  Files         150      150           
  Lines       48864    48864           
=======================================
  Hits        44763    44763           
  Misses       4101     4101
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.98% <ø> (ø)` | :arrow_up: |
| #single | `41.75% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19763?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/19763/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.22% <ø> (ø)` | :arrow_up: |

------

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