update actions upload-artifact to v4

Author: sosey

.github/workflows/build-book.yml

@@ -46,7 +46,7 @@ jobs:
 
     # Save html as artifact
     - name: Save book html as artifact for viewing
-      uses: actions/upload-artifact@v3
+      uses: actions/upload-artifact@v4
       with:
         name: book-html
         path: |