CLN: Rename raise_on_error to errors for .dtype
Title is self-explanatory.

xref #14967.

Hello @gfyoung! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/generic.py`](https://github.com/gfyoung/pandas/blob/6fb1cec49a832354e78a78c313d767d562cad8f3/pandas/core/generic.py) !

 - There are no PEP8 issues in the file [`pandas/tests/frame/test_dtypes.py`](https://github.com/gfyoung/pandas/blob/6fb1cec49a832354e78a78c313d767d562cad8f3/pandas/tests/frame/test_dtypes.py) !

 - There are no PEP8 issues in the file [`pandas/tests/series/test_dtypes.py`](https://github.com/gfyoung/pandas/blob/6fb1cec49a832354e78a78c313d767d562cad8f3/pandas/tests/series/test_dtypes.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23374?src=pr&el=h1) Report
> Merging [#23374](https://codecov.io/gh/pandas-dev/pandas/pull/23374?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f662c5f2a7b392ee96a43f055073c8523f8f0339?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23374/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23374?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #23374      +/-   ##
==========================================
- Coverage   92.22%   92.22%   -0.01%     
==========================================
  Files         169      169              
  Lines       51261    51260       -1     
==========================================
- Hits        47277    47276       -1     
  Misses       3984     3984
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.66% <100%> (-0.01%)` | :arrow_down: |
| #single | `42.22% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23374?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/23374/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.79% <100%> (-0.01%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23374?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/23374?src=pr&el=footer). Last update [f662c5f...6fb1cec](https://codecov.io/gh/pandas-dev/pandas/pull/23374?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!