TYP fixup overload in reset_index

[MarcoGorelli]

If we have t.py:

import pandas as pd

inplace: bool

reveal_type(pd.DataFrame([1,2,3]).reset_index(0, inplace=True, col_fill='a'))

then on master, the last line would be revelead as Revealed type is 'Union[pandas.core.frame.DataFrame, None]'. With the current changes, it will be revealed as Revealed type is 'None'

This function takes arguments level, drop, inplace - if drop isn't passed, then inplace needs to be passed by keyword, but level can be passed positionally

[simonjayhawkins]

Thanks @MarcoGorelli lgtm.

(If you want, no pressure, feel free to pick up #40202 if that would benefit adding overloads. I doubt I will circle back to it for a while)

[MarcoGorelli]

Thanks Simon - merging following your approval then (also, as this is really small, and serves as an example to others doing overload issues)