ci: login to dockerhub to avoid rate limiting

.github/workflows/test.yml

@@ -36,6 +36,12 @@ jobs:
           pip install -r python-requirements.txt
         working-directory: test/requirements
 
+      - name: Login to DockerHub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: Pull nginx:alpine image
         run: docker pull nginx:alpine