Update check_generated_files CI to use our published container image

[corona10]

We can do this through https://docs.github.com/en/actions/writing-workflows/choosing-where-your-workflow-runs/running-jobs-in-a-container, and it is less painful to make both image environments the same.

See: #122566 (review)
cc @erlend-aasland @hugovk @Damien-Chen

Linked PRs

• gh-125741: Update check_generated_files CI to use our published container image #125744
• [3.13] gh-125741: Update check_generated_files CI to use our published container image (gh-125744) #125759
• [3.12] gh-125741: Update check_generated_files CI to use our published container image (gh-125744) #125760
• gh-125741: Update build.yml for the new check_autoconf_regen job #125772
• [3.13] gh-125741: Update build.yml for the new check_autoconf_regen job (GH-125772) #125779
• [3.12] gh-125741: Update build.yml for the new check_autoconf_regen job (GH-125772) #130229

[nineteendo]

Can this be closed?

[corona10]

yes

[erlend-aasland]

Can this be closed?

not yet; we need the backports first

[webknjaz]

Is it documented somewhere where this image is coming from? Is there a GHA workflow producing it?

One thing to keep in mind with such containers is that you become responsible for the compatibility with GH Runners, because all the actions will start being invoked inside that runtime and so the runtime must fulfill all the toolchain expectations.