Fix: Upgrade GitHub Pages actions to non-deprecated versions

- upload-pages-artifact v2 → v3
- deploy-pages v2 → v4

Co-Authored-By: Amp <amp@ampcode.com>

Author: heikkitoivonen

.github/workflows/deploy.yml

@@ -42,7 +42,7 @@ jobs:
         run: uv run mkdocs build
 
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v2
+        uses: actions/upload-pages-artifact@v3
         with:
           path: 'site'
 
@@ -56,4 +56,4 @@ jobs:
     steps:
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v2
+        uses: actions/deploy-pages@v4