ci: bust sandbox cache (stale index)

Author: Sunrisepeak

.github/workflows/ci.yml

@@ -33,7 +33,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ~/.xlings/data/xpkgs/xim-x-mcpp/0.0.11/registry
-          key: mcpp-sandbox-${{ runner.os }}-mcpp0.0.11
+          key: mcpp-sandbox-${{ runner.os }}-mcpp0.0.11-v2
 
       - name: Build with mcpp
         run: mcpp build