`PIL.Image.getdata()` is deprecated

[brianhelba]

As of Pillow 12.1, Image.getdata() is deprecated.

This code is causing a DeprecationWarning:

pixelmatch-py/pixelmatch/contrib/PIL.py

Line 81 in 1d912f9

return [item for sublist in pil_img.convert("RGBA").getdata() for item in sublist]

This outputs with:

Image.Image.getdata is deprecated and will be removed in Pillow 14 (2027-10-15). Use get_flattened_data instead.