DM: v7.5 incorrect openapi example

[JQWong7]

Error Report

Please answer the following questions before submitting your issue. Thanks!

1. What is the URL/path of the document related to this issue?
   https://github.com/pingcap/docs/pull/15722/files
   only support few fileds.

2. How would you like to improve it?