sonarcloud: free disk space in the background in the archive build

As gate.yml does: the build starts at once and the space is free before
it needs it. The scan job's cleanup is unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/sonarcloud.yml

@@ -219,8 +219,10 @@ jobs:
         run: |
           echo "CRAFT_FONTS_DIR=$CRAFT_FONTS_PATH" >> "$GITHUB_ENV"
           echo "CRAFT_FONTS_REQUIRED=1" >> "$GITHUB_ENV"
+      # In the background, as in gate.yml: the space is free before the build needs it.
       - name: Free disk space
-        run: sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc /opt/hostedtoolcache/CodeQL
+        run: |
+          nohup sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc /opt/hostedtoolcache/CodeQL </dev/null >/dev/null 2>&1 &
       - name: Install Linux build dependencies
         uses: storytold/craft-common-actions/actions/install-apt-packages@main
         with: