docs(website): fix duplicate anchor id typo (#11311)

Author: slorber

website/docs/guides/docs/sidebar/index.mdx

@@ -191,7 +191,7 @@ To pass in custom props to a sidebar item, add the optional `customProps` object
 };
 ```
 
-## Passing a unique key {#passing-custom-props}
+## Passing a unique key {#passing-unique-key}
 
 Passing a unique `key` attribute can help uniquely identify a sidebar item. Sometimes other attributes (such as `label`) are not enough to distinguish two sidebar items from each other.