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

Author: renovate[bot]

.github/workflows/changelog.yml

@@ -19,7 +19,7 @@ jobs:
     timeout-minutes: 10
     if: "!contains(github.event.head_commit.message, 'update changelog')"
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:

.github/workflows/shellcheck-markdown.yml

@@ -14,7 +14,7 @@ jobs:
       run:
         shell: bash
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Run shellcheck
         run: |
           # test shell syntax of Markdown code snippets

.github/workflows/super-linter.yml

@@ -47,7 +47,7 @@ jobs:
       # Checkout the code base #
       ##########################
       - name: Checkout Code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           # Super-Linter requires full repository history for analysis
           fetch-depth: 0