Test failures with Pillow 10.3+

[justinmayer]

Beginning with Pillow 10.3.0, and also affecting the current 10.4.0 release, the following test failures have surfaced:

========================================================================== short test summary info ==========================================================================
FAILED pelican/plugins/image_process/test_image_process.py::test_all_transforms[image_path0-detail-transform_params10] - assert (320, 31, 792, 721) is None
FAILED pelican/plugins/image_process/test_image_process.py::test_all_transforms[image_path0-smooth_more-transform_params16] - assert (16, 0, 1016, 728) is None
FAILED pelican/plugins/image_process/test_image_process.py::test_all_transforms[image_path1-detail-transform_params10] - assert (319, 65, 740, 716) is None
FAILED pelican/plugins/image_process/test_image_process.py::test_all_transforms[image_path1-smooth_more-transform_params16] - assert (327, 72, 741, 706) is None

As a temporary measure until the source of the problem can be properly addressed, I took the liberty of adding an upward version bound for Pillow via 0231fac in #82.