free disk space in release action

.github/workflows/release.yml

@@ -44,6 +44,14 @@ jobs:
     - name: set git email
       run: git config --global user.name "${{ secrets.NBDROID_NAME }}"
 
+    - name: free disk space
+      run: |
+        sudo swapoff -a
+        sudo rm -f /swapfile
+        sudo apt clean
+        docker rmi $(docker image ls -aq)
+        df -h
+
     - name: Cache Maven packages
       uses: actions/cache@v1
       with: