ci: aggregate all builds with guardian (#51)

.github/workflows/docker-builds.yml

@@ -50,3 +50,17 @@ jobs:
           push: ${{ github.ref == 'refs/heads/master' }}
           tags: borda/docker_python-opencv-ffmpeg:${{ matrix.device }}-py${{ matrix.python_version }}-cv${{ matrix.opencv_version }}
         timeout-minutes: 240
+
+  build-guardian:
+    runs-on: ubuntu-latest
+    needs: build-push
+    if: always()
+    steps:
+      - run: echo "${{ needs.build-push.result }}"
+      - name: failing...
+        if: needs.build-push.result == 'failure'
+        run: exit 1
+      - name: cancelled or skipped...
+        if: contains(fromJSON('["cancelled", "skipped"]'), needs.build-push.result)
+        timeout-minutes: 1
+        run: sleep 90