Prevent Docker Hub login when secrets are not available

Author: m90

.github/workflows/test.yml

@@ -14,8 +14,11 @@ jobs:
 
       - name: Log in to Docker Hub
         uses: docker/login-action@v2
+        if: env.DOCKER_USERNAME
+        env:
+          DOCKER_USERNAME: ${{ secrets.DOCKER_USERNAME }}
         with:
-          username: ${{ secrets.DOCKER_USERNAME }}
+          username: ${{ env.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
 
       - name: Set up Docker Buildx