What does this MR do?
Follow-up to https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21213/diffs#note_99488777 that fixes a small issue with the list of displayed commit emails, bearing https://gitlab.com/gitlab-org/gitlab-ce/issues/51235 in mind.
We should only allow verified emails that are not the primary address to be explicitly selected.
What are the relevant issue numbers?
Does this MR meet the acceptance criteria?
Changelog entry added, if necessary
Tests added for this feature/bug
Conforms to the code review guidelines
Conforms to the merge request performance guidelines
Conforms to the style guides
Conforms to the database guides
Closes #23986 (closed)