CI: simplify ci setup a bit
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=h1) Report
> Merging [#15807](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d2f32a0362bbb90c4ab32a454962912901e32080?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/15807/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #15807      +/-   ##
==========================================
- Coverage   91.02%      91%   -0.03%     
==========================================
  Files         143      143              
  Lines       49390    49390              
==========================================
- Hits        44957    44947      -10     
- Misses       4433     4443      +10
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29tbW9uLnB5) | `90.96% <0%> (-0.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.86% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15807?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/15807?src=pr&el=footer). Last update [d2f32a0...99cd7e1](https://codecov.io/gh/pandas-dev/pandas/pull/15807?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). +1 !