Run deprecated import check before imports from other tests

[radarhere]

Fixes failures in python-pillow#6237

The test failures are because import statements like https://github.com/python-pillow/Pillow/blob/dd7cbdec95f4e8d31bc99d37ce6fb6cf7501849a/Tests/test_imageqt.py#L5 are stealing the deprecation warning. It seems that pytest runs the test files all first, before running the tests themselves.

My solution here is to

• while keeping the asserts where they are, move the import outside of the test
• rename the test file to test_deprecated_imageqt.py, moving it earlier than test_image_fromqimage.py, test_qt_image_toqimage.py, test_qt_image_qapplication.py and test_imageqt.py

[radarhere]

I've pushed another commit to upgrade to PyQt6.

[hugovk]

Thanks!