## Summary
Given a docstring like:
```py
def f(a: int, b: int) -> int:
"""Showcase function.
Parameters
----------
a : int
_description_
b : int
_description_
Returns
-------
int
_description
"""
```
We were failing to identify `Returns` as a section, because the previous
line was neither empty nor ended with punctuation. This was causing a
false negative, where by we weren't flagging a missing line before
`Returns`. So, the very reason for the rule (no blank line) was causing
us to fail to catch it.
Note that, we did have a test case for this, which was working properly:
```py
def f() -> int:
"""Showcase function.
Parameters
----------
Returns
-------
"""
```
...because the line before `Returns` "ends in a punctuation mark" (`-`).
Closes#5442.
