At least one of the GCC runs here is using the new image, 20240516.1, and it runs, so I'm assuming the change helped.

Runner Image
  Image: ubuntu-22.04
  Version: 20240516.1.0
  Included Software: https://github.com/actions/runner-images/blob/ubuntu22/20240516.1/images/ubuntu/Ubuntu2204-Readme.md

Anyway, not my favorite change. This should be removed again when our min Python version is 3.11.

What if we go another way, and ask Git to output the specific format we want, that would work for any locale settings?

I know that for multiple git commands, I already set the format I wanted, it wasn't git log, but another less common command and the usage was similar

ask Git to output the specific format we want

That's what we tried to do with requesting strict ISO.

With other things I would perhaps say yes, specifying custom format is reasonable, but going into the whole date formatting, I don't know...

What will we do when we drop Python 3.10 support? Go back to the code which is now on main or keep maintaining our own date format just for this piece of code? I say, let's work towards using ISO and this PR does that. I think it follows the trend in Python and Git: Python supported subset of ISO for parsing, now they support the whole thing. Git had some ISO-like format they called ISO and then then introduced strict ISO. Now they made change they believe is closer to the standard (I'm not convinced about that, but that's not the point here).

Is this a candidate for backporting? (On what branches the git dates were used?)

Now merged, multiple builds with Ubuntu 22.04 image 20240516.1 are successful, including ones using Python 3.8 and 3.10.

Is this a candidate for backporting? (On what branches the git dates were used?)

No, we don't plan further releases in the current branches. The only planned release in the Milestones is 8.4.0.