Re-enable pr-head

The lack of pr-head is a problem. We can't get any CI results if
there's a merge conflict. Even with no conflict, pr-merge results
change when the target branch changes, and we don't have an easy way
to see if the pull request has had a passing job once pr-merge results
become stale. So turn on pr-head.

Explicitly mark the job as non-disabled by request.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
Change-Id: I5cb3679842f2857c212d2ccfa4a4be29ba58f9eb
1 file changed