Show current user first in reviewers dropdown

What does this MR do and why?

Puts the current user first in the list for easier access when self-assigning, especially when other reviewers already added.

References

Screenshots or screen recordings

Before	After	Notes
		User is "Test User 3"
		No change when selected
		No change, keep relevance order

How to set up and validate locally

1. Open an MR as a user that would not otherwise be first in the list
2. Edit reviewers and verify your current user is first in the list of available reviewers

MR acceptance checklist

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Related to #574866