Update actions/checkout action to v6

.github/workflows/housekeeping.yml

@@ -13,7 +13,7 @@ jobs:
     name: "Markdown linting"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         name: Check out the code
       - uses: actions/setup-node@v6
         name: Setup node
@@ -25,7 +25,7 @@ jobs:
   spellchecking:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         name: Check out the code
       - uses: actions/setup-node@v6
         name: Run spell check

.github/workflows/image-optimization.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Crush images
         uses: crush-pics/crush-pics-github-action@master
         with:

.github/workflows/push-main-to-master-for-github-pages.yml

@@ -18,7 +18,7 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
     # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Push changes
       uses: ad-m/github-push-action@master
       with: