comment out Ubuntu Docker build

.github/workflows/build_docker.yaml

@@ -51,21 +51,21 @@ jobs:
         with:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
 
-      - name: Build and push Ubuntu Docker image
-        uses: docker/build-push-action@v4
-        with:
-          context: .
-          file: ./docker/ubuntu18.Dockerfile
-          push: true
-          tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:ubuntu18
-          labels: ${{ steps.meta.outputs.labels }}
-
-      - name: Prune Docker Volumes
-        shell: bash -l {0}
-        run:
-          df -h
-          docker system prune --volumes -f
-          df -h
+#      - name: Build and push Ubuntu Docker image
+#        uses: docker/build-push-action@v4
+#        with:
+#          context: .
+#          file: ./docker/ubuntu18.Dockerfile
+#          push: true
+#          tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:ubuntu18
+#          labels: ${{ steps.meta.outputs.labels }}
+#
+#      - name: Prune Docker Volumes
+#        shell: bash -l {0}
+#        run: |
+#          df -h
+#          docker system prune --volumes -f
+#          df -h
 
       - name: Build and push Rocky8 Docker image
         uses: docker/build-push-action@v4