BUG fix IntegerArray.astype int -> uint
Closes https://github.com/pandas-dev/pandas/issues/22440
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22441?src=pr&el=h1) Report
> Merging [#22441](https://codecov.io/gh/pandas-dev/pandas/pull/22441?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/68273a7a8b05049b311ea207f78e6d6f30c6eaf5?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22441/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/22441?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #22441   +/-   ##
=======================================
  Coverage   92.05%   92.05%           
=======================================
  Files         169      169           
  Lines       50733    50733           
=======================================
  Hits        46702    46702           
  Misses       4031     4031
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.46% <100%> (ø)` | :arrow_up: |
| #single | `42.24% <0%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22441?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/integer.py](https://codecov.io/gh/pandas-dev/pandas/pull/22441/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2ludGVnZXIucHk=) | `94.55% <100%> (ø)` | :arrow_up: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22441?src=pr&el=footer). Last update [68273a7...26afccf](https://codecov.io/gh/pandas-dev/pandas/pull/22441?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!