rest_framework.fields.SlugField have bug

[xuxinwen]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

1. I have defined Platform model and Its name field type is SlugField
   
2. I have defined PlatformSerializer serializer mapping to Platform
   

Expected behavior

PlatformSerializer.name.validators only have one RegexValidator validator

Actual behavior

1. I find PlatformSerializer.name.validators have two RegexValidator validators
   
2. This will lead to serializer error messages duplicate
   

[ahsanshafiq742]

Hey @auvipy @xuxinwen
I would like to work on this bug, How do i assign this issue to me?

[auvipy]

Hey @auvipy @xuxinwen
I would like to work on this bug, How do i assign this issue to me?

I'm an external contributor. you can try and come with a PR