fix(ci): set GH_REPO so labeler works without checkout

The auto-label step in pull_request_target runs without a repo
checkout, so gh pr view/edit fail with 'not a git repository'.
Setting GH_REPO points gh at the right repo without needing a
checkout step.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/label.yml

@@ -22,6 +22,7 @@ jobs:
     - name: Label PR title type
       env:
         GH_TOKEN: ${{ github.token }}
+        GH_REPO: ${{ github.repository }}
         PR_NUMBER: ${{ github.event.pull_request.number }}
         PR_TITLE: ${{ github.event.pull_request.title }}
       run: |