DOC: Fix numpydoc section underlines

[mroeschke]

e.g

/home/runner/micromamba/envs/test/lib/python3.10/site-packages/numpydoc/docscrape.py:203: UserWarning: potentially wrong underline length... 
Returns 
-------- in 

Return utc offset.... in the docstring of utcoffset
  while not self._is_at_section() and not self._doc.eof():
/home/runner/micromamba/envs/test/lib/python3.10/site-packages/numpydoc/docscrape.py:203: UserWarning: potentially wrong underline length... 
Examples 
------------ in 

Check whether all characters in each string are titlecase.... in the docstring of istitle in /home/runner/work/pandas/pandas/pandas/core/strings/accessor.py.
  while not self._is_at_section() and not self._doc.eof():

[mroeschke]

Doc checks are passing so merging