Additional tests for `Mask.to_surface`'s `area` argument

[Matiiss]

Re: #2670 (comment)

These additional tests should include:

• different mask patterns (e.g., checkerboard or just cropping some part of the mask out)
• setsurface and unsetsurface arguments both separately and together and also with different color patterns

This is the file you're looking for: https://github.com/pygame-community/pygame-ce/blob/main/test/mask_test.py
Just find tests related to to_surface in there and add your tests somewhere in that neighborhood (preferably grouping them near related existing test cases)