Check for conventional commits on merge_group events to allow rebase merges and manual edits of commit title

[dmihalcik-virtru]

The current check for conventional commit messages works with squash merges if they use the the current assigned default behavior of taking in the PR title, but this can be overridden by whoever clicks 'add to merge queue', and doesn't take into account rebase merges.

Instead, if we want to be very strict about it, we should use a commit lint checker that checks all the commits between main (the merge target) and the current temporary branch head