fix display hook error message
## What does this MR do?
Fix hook error message display.
## Are there points in the code the reviewer needs to double check?
Probably Hook will return the plain multi line text. It is better `pre` tag than `h4`.
I thought of another good looking display, but I did not come up with it. 😓
## Why was this MR needed?
When the hook returns an STDERR, "Merge in progress" button spinning forever. Due to javascript's error.
## Screenshots (if relevant)
When update hook returns an error like
```
XXXXXXXX
YYYYYYYY
ZZZZZZZZ
```
## What are the relevant issue numbers?
Closes#24020
See merge request !7775
3a66c2398a