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

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -13,7 +13,7 @@ jobs:
           bats-version: 1.2.1
 
       - name: Check out code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Test
         run: bats -r .