Update mdbook.yml

Author: cla6shade

.github/workflows/mdbook.yml

@@ -43,7 +43,7 @@ jobs:
       - name: Build with mdBook
         run: mdbook build
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v2
+        uses: actions/upload-pages-artifact@v4
         with:
           path: ./book