When the version is represented as3.13t, the--python-version option needs an operand of3.13, not3.13t.

(This, and the fix here, will automatically apply to later threaded Pythons, such as 3.14t, too.)

Before this change,in the Python 3.13t run:

+ mypy --python-version=3.13tusage: mypy [-h] [-v] [-V] [more options; see below]            [-m MODULE] [-p PACKAGE] [-c PROGRAM_TEXT] [files ...]mypy: error: argument --python-version: Invalid python version '3.13t' (expected format: 'x.y')

This isn't new--it's always happened in themypy step in the 3.13t job. We just never noticed it, because themypy step always reports failure even when working correctly, because there are a number of unresolved type errors, most of which should not be suppressed but that neither I nor others have get gotten around yet to fixing, and some of which maybe should be suppressed but neither I nor others have gotten around yet to verifying are reasonable to suppress. (For quite some time, themypy step has step-levelcontinue-on-error, which causes it not to fail the job.)

There's no connection between this and#2037 or#2038/#2039, except in the broad conceptual sense that this and#2038 share as a contributing factor that it's easy not to notice unanticipated new problems withmypy. However, just in case, I have verified that the effect of#2039 applies the same to 3.13t as to 3.13, by first testing this on a feature branch that had not integrated#2039, and then rebasing.

No change is needed intox.ini, even separately from that not yet listing apy313t environment, becausetox.ini as currently written does not pass a--python-version argument tomypy.

I plan to merge this once everything passes on CI, after also verifying again that the output is as expected.

Edit: The effect is as expected and intended. I'll just wait for the rest of CI to pass before merging.