Add MaskType to other cases

[loicdiridollou]

• Closes Check usage of Series[bool] and see if MaskType is more appropriate #868
• Tests added: Please use assert_type() to assert the type of any return value

[loicdiridollou]

There was also one other place (

pandas-stubs/pandas-stubs/core/indexes/accessors.pyi

Line 370 in af9b633

Series[bool],

) but I was a little unsure if MaskType was the appropriate behavior there, open to feedback.

[Dr-Irv]

Take a look at core/series.pyi. The logical operations like __and__(), __or__(), etc. have the same issue. Can you make the change there as well?

[Dr-Irv]

Thanks @loicdiridollou