Fix docstring in find_independent_seasons

[Illviljan]

The docstring CI is failing. For some reason the repr has changed for the function find_independent_seasons used in groupers.
Just updating it seems the easiest solution.

[jsignell]

Yeah that is really weird since the doctest docs explicitly state:

NORMALIZE_WHITESPACE is especially useful when a line of expected output is very long, and you want to wrap it across multiple lines in your source.

[keewis]

does pytest's doctest runner support NORMALIZE_WHITESPACE?

Edit: supposedly yes: https://docs.pytest.org/en/8.3.x/how-to/doctest.html#using-doctest-options

[shoyer]

thanks @Illviljan !