chore(ci): fixing docker username variable

Author: sandromodarelli

.github/workflows/release.yml

@@ -72,7 +72,7 @@ jobs:
       - name: Log in to Docker Hub
         uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3
         with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          username: ${{ vars.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_PUSH_TOKEN }}
 
       - name: Set up QEMU