Fix duplicate author showing up in autocomplete

What does this MR do?

!48668 (merged) recently changed project_members and participants_in_noteable to return an array of Users so that we can preload the status of all these users before turning them into hashes.

This changes noteable_author so that it also returns a User so that when the user is also a participant of the noteable (which they always are), participants.uniq filters them out.

This also includes the author in the user status preloading.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
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• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Related to #292892 (closed)