ci: bump github actions to Node.js 24 compatible majors

GitHub will force Node 24 on Jun 2nd 2026 and drop Node 20 entirely on
Sep 16th 2026. Upgrade every JavaScript action in the workflow to the
latest major that ships Node 24:

  actions/checkout            v4 -> v6
  actions/configure-pages     v5 -> v6
  actions/upload-pages-artifact v3 -> v5
  actions/deploy-pages        v4 -> v5

Also pin the markdown-link-check job's checkout to v6 instead of
@master, removing the upstream-can-rewrite-it risk noted earlier.

Author: ShortArrow

.github/workflows/hugo.yml

@@ -40,12 +40,12 @@ jobs:
       - name: Install Dart Sass Embedded
         run: sudo snap install dart-sass-embedded
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           submodules: recursive
       - name: Setup Pages
         id: pages
-        uses: actions/configure-pages@v5
+        uses: actions/configure-pages@v6
       - name: Install Node.js dependencies
         run: "[[ -f package-lock.json || -f npm-shrinkwrap.json ]] && npm ci || true"
       - name: Build with Hugo
@@ -58,7 +58,7 @@ jobs:
             --minify \
             --baseURL "${{ steps.pages.outputs.base_url }}/"
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v3
+        uses: actions/upload-pages-artifact@v5
         with:
           path: ./public
 
@@ -72,11 +72,11 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v4
+        uses: actions/deploy-pages@v5
   markdown-link-check:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@master
+    - uses: actions/checkout@v6
     - uses: gaurav-nelson/github-action-markdown-link-check@v1
       with:
         use-quiet-mode: no