chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/jepsen.yml

@@ -26,7 +26,7 @@ jobs:
     timeout-minutes: 120
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           submodules: recursive