Change jq query in CI scripts to Python code

[agoscinski]

In PR #6573 the readability of the jq query was criticized, but since the PR only fixes something with the query, I did not want to spent the time immediately to change it to Python.

I am honestly quite unhappy about this obscure jq syntax.
Perhaps we should switch to javascript to make this more readable. This was recommended to me here:

docker/bake-action#239 (comment)

Originally posted by @danielhollas in #6573 (comment)