Push branches for security and proposed-updates too

Use git branch -l to print the existing branches we’re interested in. This is necessary since apertis-pkg-pull-updates might have resulted in multiple branches being modified, but we don’t know in advance which ones, hence we can’t just list them all in the git push command.

Alternatively, we could have used : specifier, which pushes all "matching" branches, but it wouldn’t have worked for us in this case as apertis-pkg-pull-updates can create new branches which don’t yet have corresponding counterparts.

Another approach would be to push the current branch, but that would discount other branches that could have been modified too.

Finally, we could have used --all, but that would risk pushing something unrelated if the CI cleanup failed for some reason and had other cached branches.