chore(deps): update actions/upload-pages-artifact action to v4

Author: renovate[bot]

.github/workflows/ci.yml

@@ -50,7 +50,7 @@ jobs:
         name: Build the site
         run: mkdocs build
       - name: Upload Pages artifact
-        uses: actions/upload-pages-artifact@v3
+        uses: actions/upload-pages-artifact@v4
         with:
           name: build-pr${{ github.event.pull_request.number }}
           path: site
@@ -114,7 +114,7 @@ jobs:
         name: Build the site
         run: mkdocs build
       - name: Upload Pages artifact
-        uses: actions/upload-pages-artifact@v3
+        uses: actions/upload-pages-artifact@v4
         with:
           name: build-${{ github.ref_name }}-${{ github.run_id }}
           path: site