BUG: Matplotlib scatter datetime
xref https://github.com/matplotlib/matplotlib/issues/11391
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22039?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@4cf95ba`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22039/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/22039?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #22039   +/-   ##
=========================================
  Coverage          ?      92%           
=========================================
  Files             ?      170           
  Lines             ?    50611           
  Branches          ?        0           
=========================================
  Hits              ?    46567           
  Misses            ?     4044           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.41% <100%> (?)` | |
| #single | `42.19% <0%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22039?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/22039/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.88% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22039?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/22039?src=pr&el=footer). Last update [4cf95ba...0132fea](https://codecov.io/gh/pandas-dev/pandas/pull/22039?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @TomAugspurger 