Add testing on Python 3.14

[ngoldbaum]

I suspect there will be new CI failures on Linux, but the same test has been failing for the past two weeks on Windows (see #1128). It's marked as flaky and I've seen it pass on CI sometimes. Not sure if you're comfortable adding new jobs that fail.

[ngoldbaum]

Hmm, the tests on Windows for 3.14t failed in a slightly different way compared with the others:

tests/test_0_watchmedo.py::test_invalid_verbosity[verbosity_cmdline_args10-cmdline0] PASSED [ 32%]
tests/test_0_watchmedo.py::test_invalid_verbosity[verbosity_cmdline_args10-cmdline1] PASSED [ 33%]
tests/test_0_watchmedo.py::test_tricks_from_file[tricks-from] ROOT: [10160] KeyboardInterrupt - teardown started
py: exit 1 (750.59 seconds) D:\a\watchdog\watchdog> python -m pytest pid=9960
  py: FAIL code 1 (802.96 seconds)
  evaluation failed :( (821.82 seconds)
Error: The operation was canceled.

[BoboTiG]

Multiple tests are flaky, yes. I do not know how to deal with those, since it implies having a stable OS firing events "in order". Maybe the situation can be improved, I'm open to ideas/PR.

About adding new jobs, lets do it :)