failing to apply PR patch should be reported in PR

[boegel]

When setting up the working directory for jobs, the PR patch that is used may fail to apply because of recent changes in the target branch (see for example EESSI/software-layer#321 (comment)):

[20230906-T07:10:52] run_cmd(): Error running 'git apply 321.diff' in '/mnt/shared/home/bot/eessi-bot-software-layer/jobs/2023.09/pr_321/event_7f6fa000-4c84-11ee-97ce-9db16087e54d/run_000/linux_x86_64_generic/eessi-2023.06-software
           stdout ''
           stderr 'error: patch failed: configure_easybuild:26
error: configure_easybuild: patch does not apply
'

This implies that the PR should be synced with the target branch first.

The bot should post a comment in the PR when it fails to prepare the working directory for build jobs, now this is failing silently (no build jobs are being submitted, and it's unclear why).

[boegel]

Same problem occurred in EESSI/software-layer#330 because EESSI/software-layer#329 got merged before build was (re-)triggered, because both are touching .github/workflows/test_eessi.yml

[trz42]

I don't think it's a bug, but letting the bot report the result of the failing patch is certainly a worthwhile improvement.

[Neves-P]

I've got the bot running now up to a point where I should be able to replicate this on my end, so I can start working on this issue now.