Make not finding the PR an error #925

Description:
I would like an input so I can decide that this error 👇 should be an error and not a warning.

Justification:
It is easy to break things such that PRs can't be found (e.g. moving to least-permissions and accidentally removing read access). When this happens, there is no feedback that labeler has stopped working; you can only find this warning if you go look for it.

We have additional automation that runs based on labels, When labeler fails, that automation does the wrong thing. For example, we require 2 approvals on PRs with the Migration label, which is added by labeler based on files changed. When it fails, the PR doesn't get the label, and we allow it to merge with only 1 approval.

Are you willing to submit a PR?
Sure.