ci: add ci/skip/multi-arch-build label

If the `ci/skip/multi-arch-build` label is set on a PR, the GitHub
Workflow only builds for the local architecture. This makes it possible
to merge PRs faster.

Signed-off-by: Niels de Vos <ndevos@redhat.com>

.github/workflows/build-multi-stage.yaml

@@ -15,7 +15,13 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: multi-arch-build
+        # yamllint disable-line rule:line-length
+        if: ${{ ! contains(github.event.pull_request.labels.*.name, 'ci/skip/multi-arch-build') }}
         # podman cannot pull images with both tag and digest
         # https://github.com/containers/buildah/issues/1407
         # use docker to build images
         run: CONTAINER_CMD=docker ./scripts/build-multi-arch-image.sh
+      - name: single-arch-build
+        # yamllint disable-line rule:line-length
+        if: ${{ contains(github.event.pull_request.labels.*.name, 'ci/skip/multi-arch-build') }}
+        run: make containerized-build