fix: CI chown act cache to prevent false build failure

The checkout action post-cleanup fails on root-owned files in the
workspace, marking the build as failed even though the ISO was built.
Chown the entire act cache dir so cleanup succeeds.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-iso.yml

@@ -108,4 +108,6 @@ jobs:
 
       - name: Fix workspace permissions
         if: always()
-        run: sudo chown -R $(id -u):$(id -g) . 2>/dev/null || true
+        run: |
+          sudo chown -R $(id -u):$(id -g) . 2>/dev/null || true
+          sudo chown -R $(id -u):$(id -g) "$HOME/.cache/act" 2>/dev/null || true