user-event: Update api-keyboard.mdx (#1172)

Author: lsoares

docs/user-event/api-keyboard.mdx

@@ -35,7 +35,7 @@ Keystrokes can be described:
   prefixing them with a backslash `\`.
 
   ```js
-  keyboard('{}}') // translates to: }
+  keyboard('{\}}') // translates to: }
   ```
 
 - Per