Regression on code changes and message changes

Identified in PR https://github.com/checkstyle/checkstyle/pull/4903 ,

If a PR makes changes to Check logic and changes to a existing message, normal regression will display too many differences as all will be centered around change in message and it will be impossible/hard to discern if any where from code changes.

In this situation, we should force check's message to a specific message for both base and patch runs so only the differences in the code is examined.
Example of configuration for the PR mentioned:
````

````
Notice the message is only for `summary.first.sentence` as that was what was modified in the PR.