Update _blog.yml (#2770)

Author: hannahblair

_blog.yml

@@ -5743,7 +5743,7 @@
 - local: gradio-dataframe-upgrade 
   title: "Introducing Gradio's new Dataframe!"
   author: hmb
-  thumbnail: /blog/assets/gradio-dataframe-upgrade/thumbnail.png  
+  thumbnail: /blog/assets/gradio-dataframe-update/thumbnail.png  
   date: March 24, 2025
   tags:
     - gradio