Improved support for Python 3.14

[radarhere]

1. A test has started failing now that an error message has changed in Python 3.14

https://github.com/python-pillow/Pillow/actions/runs/14903027962/job/41859109942#step:11:3834

E AssertionError: Regex pattern did not match.
E Regex: 'must be sequence of length 4'
E Input: 'argument 3 must be tuple of length 4, not 2'

2. An error has started occurring when building PyQt6 on Python 3.14 - https://github.com/python-pillow/Pillow/actions/runs/14903027971/job/41859749652#step:8:12

Let's skip it for now.

3. Those changes then triggers our Windows message about unsupported Python versions - https://github.com/python-pillow/Pillow/actions/runs/14906195788/job/41869036883?pr=8948#step:28:779. Since Python 3.14 has now reached beta, we would like users to be able to install and it, so let's increment the version check.

...this then leads to the same error from building PyQt6 occurring when building Pillow - https://github.com/python-pillow/Pillow/actions/runs/14906674076/job/41870606277?pr=8948#step:28:769

LINK : fatal error LNK1104: cannot open file 'python314t.lib'