support master tag for building of example app

Author: n0str

.github/workflows/build-demo.yml

@@ -50,4 +50,4 @@ jobs:
           file: docker/Dockerfile.demo
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
-          push: ${{ startsWith(github.ref, 'refs/tags/v') }}
+          push: ${{ startsWith(github.ref, 'refs/tags/v') || endsWith(github.ref, '/master') }}