TST: Mark test_pct_max_many_rows with pytest.mark.single
- [X] closes #23726
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

See this comment for context: https://github.com/pandas-dev/pandas/issues/23726#issuecomment-440076164
Hello @jschendel! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/frame/test_rank.py`](https://github.com/jschendel/pandas/blob/2c05f5a63c946414f548a13a76f8ea3cc3babe69/pandas/tests/frame/test_rank.py) !

 - There are no PEP8 issues in the file [`pandas/tests/series/test_rank.py`](https://github.com/jschendel/pandas/blob/2c05f5a63c946414f548a13a76f8ea3cc3babe69/pandas/tests/series/test_rank.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_algos.py`](https://github.com/jschendel/pandas/blob/2c05f5a63c946414f548a13a76f8ea3cc3babe69/pandas/tests/test_algos.py) !

 thanks @jschendel  # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23799?src=pr&el=h1) Report
> Merging [#23799](https://codecov.io/gh/pandas-dev/pandas/pull/23799?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/deb7b4d5003b939f47e525bcdaceeea48622a73a?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23799/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23799?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23799   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files         161      161           
  Lines       51451    51451           
=======================================
  Hits        47483    47483           
  Misses       3968     3968
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.68% <ø> (ø)` | :arrow_up: |
| #single | `42.31% <ø> (+0.03%)` | :arrow_up: |


------

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> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23799?src=pr&el=footer). Last update [deb7b4d...2c05f5a](https://codecov.io/gh/pandas-dev/pandas/pull/23799?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
