TST: Don't assert that a bug exists in numpy
Better to ignore the warning from the bug, rather than assert the bug is still there

After this change, numpy/numpy#9412 _could_ be backported to fix the bug
Hello @eric-wieser! Thanks for submitting the PR.

 - In the file [`pandas/tests/test_algos.py`](https://github.com/pandas-dev/pandas/blob/3444dc219c75461fec6b69381576de46892aaaf5/pandas/tests/test_algos.py), following are the PEP8 issues :

> [Line 392:9](https://github.com/pandas-dev/pandas/blob/3444dc219c75461fec6b69381576de46892aaaf5/pandas/tests/test_algos.py#L392): [E741](https://duckduckgo.com/?q=pep8%20E741) ambiguous variable name 'l'

 Hey @pep8speaks, I didn't even touch that line.

(I know you're a bot) # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=h1) Report
> Merging [#16940](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ad24759871ea43131711cfce1e5fc69c06d82956?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16940/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16940      +/-   ##
==========================================
- Coverage   90.99%   90.98%   -0.02%     
==========================================
  Files         161      161              
  Lines       49306    49306              
==========================================
- Hits        44868    44859       -9     
- Misses       4438     4447       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <ø> (ø)` | :arrow_up: |
| #single | `40.19% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.71% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16940?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/16940?src=pr&el=footer). Last update [ad24759...3444dc2](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=h1) Report
> Merging [#16940](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ad24759871ea43131711cfce1e5fc69c06d82956?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16940/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16940      +/-   ##
==========================================
- Coverage   90.99%   90.98%   -0.02%     
==========================================
  Files         161      161              
  Lines       49306    49306              
==========================================
- Hits        44868    44859       -9     
- Misses       4438     4447       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <ø> (ø)` | :arrow_up: |
| #single | `40.19% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.71% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16940?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/16940?src=pr&el=footer). Last update [ad24759...3444dc2](https://codecov.io/gh/pandas-dev/pandas/pull/16940?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @eric-wieser sorry about the bots. Should be fixed by https://github.com/pandas-dev/pandas/pull/16944. Thanks! > (I know you're a bot)

they never listen :>

@eric-wieser thanks for fixing

also https://github.com/numpy/numpy/issues/641 is relevant on the numpy side (this is what safe_sort is fixing in fact)