fix line break formatting in flush example

Author: cellog

fern/assistants/flush-syntax.mdx

@@ -53,8 +53,12 @@ VAPI supports three flush formats with case-insensitive matching:
 <CodeBlocks>
   ```html title="Self-closing (Recommended)"
   <flush />
-  ``` ```html title="Opening tag"
-  <flush>``` ```html title="Closing tag"</flush>
+  ```
+  ```html title="Opening tag"
+  <flush>
+  ```
+  ```html title="Closing tag"
+  </flush>
   ```
 </CodeBlocks>