Add python3 as a dep so g-ir-scanner can run

[murraybd]

g-ir-scanner would previously fail to run because python3 was not available.

[smoser]

This isn't right. We need to fix the shbang so it uses the Python that it was installed for.

A python3 drop will Get you a /usr/bbin/python3, but not necessarily the right python3.

See my issue for unversioned Python and 313. Also related here is the python-as wrapper, it works likely fix this.

[dannf]

For reference, here's the issue @smoser is referring to - #37197
According to that, I think we want to try to use the suggestion in the "pick a specific version" example, and then fallback to the python-as-wrapper thing if it fails to inherit a python3.13 shbang.

[smoser]

For reference, here's the issue @smoser is referring to - #37197

According to that, I think we want to try to use the suggestion in the "pick a specific version" example, and then fallback to the python-as-wrapper thing if it fails to inherit a python3.13 shbang.

If we land Python-as-wrapper (#36891) we can use that. I do think it's useful to generally "do the right thing".

[murraybd]

I'm going to close this in favor of sil2100's PR at #37393.