imageio v2.33.0 requieres Pillow>=9.1.0 for GIFs

[sitic]

When using Pillow<9.1.0 (pip install pillow==9.0.1 imageio) importing a GIF fails:

import imageio.v3 as iio3
iio3.imread('https://upload.wikimedia.org/wikipedia/commons/8/8f/Example.gif')

error:

Traceback (most recent call last):
  File "imageio/v3.py", line 54, in imread
    return np.asarray(img_file.read(**call_kwargs))
  File "imageio/plugins/pillow.py", line 238, in read
    GifImagePlugin.LoadingStrategy.RGB_AFTER_DIFFERENT_PALETTE_ONLY
AttributeError: module 'PIL.GifImagePlugin' has no attribute 'LoadingStrategy'

PIL.GifImagePlugin.LoadingStrategy was added to Pillow in v9.1.0. This works with imageio<2.33.

[Pandede]

Importing LoadingStrategy is due to this issue #1030 and I fixed it according to this PR python-pillow/Pillow#6150.

I may make a PR to lock the mode to RGB when loading the GIF if Pillow<9.1.0 (same as set LoadingStrategy to RGB_ALWAYS).