Update step name to be more clear about intent

.github/workflows/dockerbuild.yml

@@ -13,7 +13,7 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v3
 
-      - name: Build and push Docker image
+      - name: Build and validate ffmpeg
         uses: docker/build-push-action@5cd11c3a4ced054e52742c5fd54dca954e0edd85
         with:
           context: src/