API change reviews can't update cleanly now that each Qt module gets its own commit

QTQAINFRA-4763 changed the API change review scripts to produce one commit per Qt module, within each git module. Previously, api-review-gen supported updating the monolithic commit per git module when a new version of the branch on its way to release was available. However, that's broken by having one commit per Qt module: only the last commit in the branch is available to git commit --amend, so the update can't fix up the earlier commits. This has severely broken the update process for API change reviews.

This can be fixed by making each new commit, of a Qt module, be a git commit --fixup for the earlier commit for the same Qt module (when there is one), then ending the process with a git rebase --autosquash.