ci: semver-check action doesn't run on PRs from same repo

[jschwe]

While testing a CI change I noticed that the pull_request_target trigger means that branches pushed to this fork, will not trigger pull_request_target PR checks, hence the semver labels can't be applied.

[jschwe]

hmm, maybe this does work and it was just the github actions outage causing the job to be delayed? I'll need to double-check that tommorow once actions works reliably again...