Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set up cargo cache
       uses: actions/cache@v4
       continue-on-error: false