Can't specify python version for testing of built dists

[tepickering]

I don't see any examples of how to specify a python version for running tests. In looking at the workflow itself, it looks like it's hard-coded to 3.x. I have dependencies that still don't support 3.10 so need to stick with 3.9 for now. With my normal tox testing workflow, this isn't an issue. My workaround is to not use testing in the build workflow, but it would be nice to as an extra consistency check.

[astrofrog]

I agree we should support specifying the Python version!