DOC: Fixup docstring [ci skip]
[ci skip]
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21663?src=pr&el=h1) Report
> Merging [#21663](https://codecov.io/gh/pandas-dev/pandas/pull/21663?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e0f978d43c960e0af7944a9d7d410662e071c0c7?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/21663/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21663?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21663   +/-   ##
=======================================
  Coverage    91.9%    91.9%           
=======================================
  Files         154      154           
  Lines       49555    49555           
=======================================
  Hits        45542    45542           
  Misses       4013     4013
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.27% <ø> (ø)` | :arrow_up: |
| #single | `42.03% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21663?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/21663/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.19% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21663?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/21663?src=pr&el=footer). Last update [e0f978d...f800acf](https://codecov.io/gh/pandas-dev/pandas/pull/21663?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
