docs: fix typo in self-hosting example (#22519)

docs/usage/examples/self-hosting.md

@@ -95,7 +95,7 @@ stringData:
   RENOVATE_TOKEN: 'your-github-enterprise-renovate-user-token'
 ```
 
-A `config.js` file can be added to the manifest using a `ConfigMap` as shown in the following example (using a "dry run" in github.com):
+A `config.json` file can be added to the manifest using a `ConfigMap` as shown in the following example (using a "dry run" in github.com):
 
 ```yaml
 ---