fix: add missing docker login for release process

.github/workflows/release.yml

@@ -25,6 +25,12 @@ jobs:
         with:
           ruby-version: 2.6
 
+      - name: Login to Docker Hub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
       - name: install package_cloud
         run: gem install package_cloud