Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       # For GitHub Comment Reporter
       # https://megalinter.io/latest/reporters/GitHubCommentReporter/
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       # MegaLinter
       - name: MegaLinter
@@ -53,7 +53,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Guix cache
         uses: actions/cache@v4