BUG: Ignore versionadded directive when checking for periods at docstring end
Will ignore the `versionadded` directive when checking for `'.'` at the end of descriptions.  

- [x] closes #22405
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Can you add a test case for this? We also have a versionchanged directive which we should account for here And the `deprecated` directive as well probably. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22423?src=pr&el=h1) Report
> Merging [#22423](https://codecov.io/gh/pandas-dev/pandas/pull/22423?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/140c7bbda7aba8e9ac36a66a694234c9b1be4f95?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/22423/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/22423?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22423      +/-   ##
==========================================
- Coverage   92.05%   92.04%   -0.01%     
==========================================
  Files         169      169              
  Lines       50714    50740      +26     
==========================================
+ Hits        46684    46705      +21     
- Misses       4030     4035       +5
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <ø> (-0.01%)` | :arrow_down: |
| #single | `42.24% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22423?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/\_depr\_module.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlcHJfbW9kdWxlLnB5) | `65.11% <0%> (-2.33%)` | :arrow_down: |
| [pandas/core/reshape/pivot.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9waXZvdC5weQ==) | `96.55% <0%> (-0.63%)` | :arrow_down: |
| [pandas/core/arrays/integer.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2ludGVnZXIucHk=) | `94.55% <0%> (-0.12%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `85.75% <0%> (-0.11%)` | :arrow_down: |
| [pandas/core/reshape/merge.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZXJnZS5weQ==) | `94.15% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/groupby/grouper.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9ncm91cGVyLnB5) | `98.16% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.44% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.24% <0%> (-0.01%)` | :arrow_down: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `93.73% <0%> (ø)` | :arrow_up: |
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.48% <0%> (ø)` | :arrow_up: |
| ... and [5 more](https://codecov.io/gh/pandas-dev/pandas/pull/22423/diff?src=pr&el=tree-more) | |

------

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