Drop Python 3.9 from the `justfile` matrix

[nathanjmcdougall]

just test-python still tries to test against Python 3.9, but support is now dropped as of 3.14. This should be removed

grimp/justfile

Lines 38 to 40 in 82ebd22

	[group('testing')]
	test-python-3-9:
	UV_PYTHON=3.9 just test-python

Details

UV_PYTHON=3.9 just test-python
Using CPython 3.9.21
error: The requested interpreter resolved to Python 3.9.21, which is incompatible with the project's Python requirement: `>=3.10` (from `project.requires-python`)
error: Recipe `test-python` failed on line 31 with exit code 2
error: Recipe `test-python-3-9` failed on line 40 with exit code 2
error: Recipe `full-check` failed on line 171 with exit code 2

[seddonym]

Thanks for suggestion - have tweaked this in #280, feel free to review!