DEPR: passing categories or ordered kwargs to Series.astype is deprecated
closes #17636

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17742?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@a3d538a`). [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/17742/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/17742?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #17742   +/-   ##
=========================================
  Coverage          ?   91.23%           
=========================================
  Files             ?      163           
  Lines             ?    49859           
  Branches          ?        0           
=========================================
  Hits              ?    45490           
  Misses            ?     4369           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.03% <100%> (?)` | |
| #single | `40.25% <50%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17742?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/17742?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `94.38% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17742?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/17742?src=pr&el=footer). Last update [a3d538a...cbaa585](https://codecov.io/gh/pandas-dev/pandas/pull/17742?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 There seem to be still quite some warnings of using this in our own tests, see eg https://travis-ci.org/pandas-dev/pandas/jobs/282520540