CI: Ensure that github containers match the official binaries

The binaries accidentally included VCS information whereas binaries
built from the release tarball do not. For consistency remove the .git
directory before building the container on Github.

.github/workflows/docker.yml

@@ -47,6 +47,13 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@f95db51fddba0c2d1ec667646a06c2ce06100226
 
+      - name: Ensure consistent binaries
+        run: |
+          echo "removing git directory for consistency with release binaries"
+          rm -rf .git
+        # remove VCS information from release builds, keep VCS for nightly builds on master
+        if: github.ref != 'refs/heads/master'
+
       - name: Build and push Docker image
         uses: docker/build-push-action@f2a1d5e99d037542a71f64918e516c093c6f3fc4
         with: