Automatically comment on PR template CI failure

[MattIPv4]

As a follow-up to #9782 (#9449), it'd be great to extend the workflow such that when the workflow fails, it leaves a comment on the PR explaining to the user what failed in their PR template, and what information they need to add to it (in the correct format). We should make sure that subsequent runs update the existing comment, rather than repeatedly posting new comments.

[indus]

The splitting and execution sequence of the checks may be a somewhat critical point. The tests are executed in their predefined order and only start when a previous one has run successfully. This would lead to deferred error messages. From a requesters point of view, it would probably be best if there was only a single validation step that comments all the discrepancies at once.