fix(ci): use current PR's branch

As we don't have the required checks anymore, this will only ever be
executed on the PR and therefore work without having to fall back to the
default_branch

.github/workflows/validate-and-label-pullrequest.yaml

@@ -30,7 +30,8 @@ jobs:
  steps:
  - uses: actions/checkout@v3
  with:
- ref: ${{ github.event.repository.default_branch }}
+ fetch-depth: 0
+ ref: ${{ github.event.pull_request.head.sha }}
 
  - uses: helm/[email protected]
  - run: .github/scripts/validate-and-label-pullrequest.sh