fix: bust Linux xlings cache to pick up mcpp@0.0.16

Stale cache had mcpp@0.0.13 which lacks `self config --mirror`.
Bump cache key suffix to force fresh install of mcpp@0.0.16.

Author: Sunrisepeak

.github/workflows/ci.yml

@@ -49,9 +49,9 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ~/.xlings
-          key: xlings-${{ runner.os }}-${{ hashFiles('.xlings.json') }}
+          key: xlings-${{ runner.os }}-v2-${{ hashFiles('.xlings.json') }}
           restore-keys: |
-            xlings-${{ runner.os }}-
+            xlings-${{ runner.os }}-v2-
 
       - name: Bootstrap mcpp via xlings
         env: