Mark test_pct_max_many_rows as high memory
Fixes issue #25384

- [ ] closes #25384
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=h1) Report
> Merging [#25400](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9c0f6a8d703b6bee48918f2c5d16418a7ff736e3?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25400/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25400      +/-   ##
==========================================
+ Coverage   91.73%   91.73%   +<.01%     
==========================================
  Files         173      173              
  Lines       52845    52845              
==========================================
+ Hits        48479    48480       +1     
+ Misses       4366     4365       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <ø> (ø)` | :arrow_up: |
| #single | `41.69% <ø> (-0.04%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25400/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `87.66% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25400?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/25400?src=pr&el=footer). Last update [9c0f6a8...5a73ff8](https://codecov.io/gh/pandas-dev/pandas/pull/25400?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/25400?src=pr&el=h1) Report
> Merging [#25400](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9c0f6a8d703b6bee48918f2c5d16418a7ff736e3?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/25400/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #25400      +/-   ##
==========================================
+ Coverage   91.73%   91.73%   +<.01%     
==========================================
  Files         173      173              
  Lines       52845    52845              
==========================================
+ Hits        48479    48480       +1     
+ Misses       4366     4365       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <ø> (ø)` | :arrow_up: |
| #single | `41.69% <ø> (-0.04%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/25400/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `87.66% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25400?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/25400?src=pr&el=footer). Last update [9c0f6a8...5a73ff8](https://codecov.io/gh/pandas-dev/pandas/pull/25400?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @scarabeusiv (I realized we have ``run-high-memory`` option) can you send a followup PR to enable this option on the CI for a single build is fine I would not mind doing it but I am not sure which file in the end I should edit the ci/run_tests.sh seems the most obvious? see .travis.yml 

and how we trigger slow builds 