Update GitHub Actions versions.

Author: davidchisnall

.github/workflows/main.yml

@@ -49,7 +49,7 @@ jobs:
           JEKYLL_ENV: production
       - name: Upload artifact
         # Automatically uploads an artifact from the './_site' directory by default
-        uses: actions/upload-pages-artifact@v2
+        uses: actions/upload-pages-artifact@v3
 
   # Deployment job
   deploy:
@@ -61,4 +61,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v2
+        uses: actions/deploy-pages@v4