fix: free space during workflow (#12350)

### What

Github workflow is failing on the following PR:
#12262

Due to 
> ##[error]Error: Command failed: docker save
openfoodfacts-server/backend:dev -o
/tmp/openfoodfacts-server_backend_dev
> write /tmp/.docker_temp_901694671: no space left on device

The following PR attempt to free some space before to call
"ishworkh/[email protected]" step in
"build_backend:" job

### Screenshot
<img width="1332" height="650" alt="Screenshot_20250907_221917"
src="https://github.com/user-attachments/assets/c4e9b6cc-851b-44c0-974e-09277d537677"
/>

### Related issue(s) and discussion
- Fixes #-none-

Author: benbenben2

.github/workflows/pull_request.yml

@@ -89,6 +89,17 @@ jobs:
         restore-keys: taxonomies-
     - name: build
       run: make build container=backend
+    - name: Free disk space
+      run: |
+        echo "Before cleanup:"
+        df -h
+        docker system prune -f || true
+        sudo rm -rf /usr/local/lib/android || true
+        sudo rm -rf /opt/ghc || true
+        sudo rm -rf /usr/share/dotnet || true
+        sudo rm -rf /usr/local/share/boost || true
+        echo "After cleanup:"
+        df -h
     - name: push backend image as artifact
       uses: ishworkh/[email protected]
       with: