Fix duplicate reviewers in gh pr edit by passing logins as defaults

Use DefaultLogins instead of Default display names when calling
MultiSelectWithSearch for reviewers. The dedup logic in the
prompter compares keys (logins) against defaults, so passing
display names like 'mxie (Melissa Xie)' prevented deduplication
against search result keys like 'mxie'.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: BagToad

pkg/cmd/pr/shared/editable.go

@@ -317,7 +317,7 @@ func EditFieldsSurvey(p EditPrompter, editable *Editable, editorCommand string)
 			editable.Reviewers.Value, err = p.MultiSelectWithSearch(
 				"Reviewers",
 				"Search reviewers",
-				editable.Reviewers.Default,
+				editable.Reviewers.DefaultLogins,
 				// No persistent options - teams are included in search results
 				[]string{},
 				editable.ReviewerSearchFunc)