Disable python 3.9 coverage in CI as it can get the wrong line numbers resulting in unsolvable coverage errors, as it conflicts with 3.10+.

pep-0626 (3.10) introduced accurate line number tracking.

There's an example of 3.9 getting the wrong line number intests/test_direct.py which is now covered with a# pragma: no cover

This was discovered when developing the AG-UI feature, where multipleifelif blocks were flagged covered by 3.9 but not by other versions, which resulted in failure cycle of not covered and incorrectly marked as not covered.