[WIP]DOC: Fixed more warnings
Also trying to fail on warnings. I think it's not working yet.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20542?src=pr&el=h1) Report
> Merging [#20542](https://codecov.io/gh/pandas-dev/pandas/pull/20542?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c4b4a81f56205082ec7f12bf77766e3b74d27c37?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20542/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/20542?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20542      +/-   ##
==========================================
+ Coverage   91.81%   91.84%   +0.02%     
==========================================
  Files         152      152              
  Lines       49259    49260       +1     
==========================================
+ Hits        45229    45242      +13     
+ Misses       4030     4018      -12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <ø> (+0.02%)` | :arrow_up: |
| #single | `41.89% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20542?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/20542/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.85% <0%> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/20542/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.81% <0%> (+1.73%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20542?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/20542?src=pr&el=footer). Last update [c4b4a81...230c29a](https://codecov.io/gh/pandas-dev/pandas/pull/20542?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 I've removed the changes to the DocBuilder with the errors since I haven't been able to get it working yet. I'll try again once we're error free. Merging. Down to 2 warnings now.

```
/tmp/doc/source/index.rst.rst: WARNING: file not found: 'pandas.pdf'
/tmp/doc/source/index.rst.rst: WARNING: file not found: 'pandas.zip'
``` The warnings sound very much like https://github.com/spatialaudio/nbsphinx/issues/174, feel free to contribute there. Ah, interesting, I'll take a look.

In this case the files really may not exist, since we don't do the PDF builds on our CI. @TomAugspurger I assume the warning is caused by this:

https://github.com/pandas-dev/pandas/blob/6d610a4d9393c0d0335267dc3252ccabb9e51e43/doc/source/index.rst.template#L7-L9

... which would be exactly the same case as https://github.com/spatialaudio/nbsphinx/issues/174.