Fix GitHub Actions workflow: update to non-deprecated action versions

- actions/configure-pages@v3 → v4
- actions/upload-pages-artifact@v2 → v3
- actions/deploy-pages@v2 → v4

Author: alistairewj

.github/workflows/deploy-jekyll.yml

@@ -38,7 +38,7 @@ jobs:
 
       - name: Setup Pages
         id: pages
-        uses: actions/configure-pages@v3
+        uses: actions/configure-pages@v4
 
       - name: Build with Jekyll
         run: |
@@ -48,7 +48,7 @@ jobs:
           JEKYLL_ENV: production
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v2
+        uses: actions/upload-pages-artifact@v3
         with:
           path: ./jekyll-site/_site
 
@@ -63,4 +63,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v2
+        uses: actions/deploy-pages@v4