Pull Request : The reviewer is selected automatically when tabbed out of the search field

Issue Summary

When the user tabs out of the search field for the reviewer dropdown menu, the top available reviewer is selected automatically.

Tested URL:

https://instenv-17238-xigc.instenv.internal.atlassian.com/projects/TEST/repos/test1/pull-requests?state=ALL&reviewer=admin 
Platform: Bitbucket Datacenter

Version: 7.21.0

Steps to Reproduce

1. Launch the URL
2. Navigate to the Reviewer dropdown menu and "Enter" on the Reviewer link and then press "Tab" of "Shift + Tab" to move out of the search field.

Screen recording 

Screen Recording 2022-04-14 at 6.15.03 PM.mov

Actual Results

When the user navigates into the reviewer link and the focus is on the search input field, and the user presses the "Tab" or "Shift + Tab" key, a random user is selected which is on the top of the list in the suggested list for reviewers.
When a random user is selected, unwanted pull request details appear on the page that the user is unaware of.

This will create confusion for the assistive technology user and would make them reselect all the filters. 

Expected Results

When the user tabs out of the search input field with "Tab" or "Shift + Tab", the focus should move out without selecting any reviewer.
The reviewer should only be selected when the user has the focus on the respective reviewer in the list and "Enter" is pressed.

Workaround

Currently, there is no known workaround for this behaviour. A workaround will be added here when available