Update upload-pages-artifact version https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/

Author: hokeun

.github/workflows/mdbook.yml

@@ -43,7 +43,7 @@ jobs:
       - name: Build with mdBook
         run: mdbook build .
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v1
+        uses: actions/upload-pages-artifact@v4
         with:
           path: ./book/