This broke when we moved the check-cherry-picks workflow into the bigger
PR workflow. At this time, the "workflow run" became the whole PR
workflow, which includes many more than just 1 job, thus the assumption
in `jobs[0]` doesn't hold anymore.
Most of the checks we do for cherry-picks are dismissable warnings, with
one exception: When a commit hash has been found, but this hash is not
available in any of the pickable branches, we raise this with
severity=error. This should also *block* the merge and not be
dismissable. That's because this is a fixable issue in every case.
Previously, when the diff contained a context line with ```, this would
end the code block and entirely break the markdown rendering.
Now we use the html code blocks provided by `core.summary` and properly
escape the content, so that it never escapes via html tags.
This reduces noise that the cherry-pick reviews produce when formatting
related conflicts had to be resolved. We only do this in the
length-limited review comment, though. All changes, including
whitespace, can still be double-checked in the job log if needed.
This turns the check-cherry-pick script into a github-script based
JavaScript program. This makes it much easier to extend to check reverts
or merge commits later on.
