Use CSV for output tags of docker meta action (#71)

Signed-off-by: Andreas Heinrich <andreas.heinrich@rwth-aachen.de>

Author: andistorm

.github/workflows/continuous_integration.yml

@@ -276,6 +276,7 @@ jobs:
         uses: docker/metadata-action@v5
         with:
           images: ${{ env.BUILD_KIT_IMAGE_NAME }}
+          sep-tags: ","
       - name: Setup Docker buildx
         uses: docker/setup-buildx-action@v3
       - name: Build