Change default disabled merge request widget message to be more general

What does this MR do?

EE MR, https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3180

Change default disabled merge request widget message to be more general

Before	After

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The message about pipelines not succeeding yet is not accurate when we can't merge because of approvers.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #39188 (closed)