fix(survey): use useReviewerSearch consistently in prompt path

The reviewer prompt branch checked reviewerSearchFunc != nil directly
instead of useReviewerSearch, making the fetch and prompt decisions
inconsistent. This mirrors how the assignee path already uses
useAssigneeSearch at both the fetch and prompt gates.

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

Author: BagToad

pkg/cmd/pr/shared/survey.go

@@ -263,7 +263,7 @@ func MetadataSurvey(p Prompt, io *iostreams.IOStreams, baseRepo ghrepo.Interface
 	}{}
 
 	if isChosen("Reviewers") {
-		if reviewerSearchFunc != nil {
+		if useReviewerSearch {
 			selectedReviewers, err := p.MultiSelectWithSearch(
 				"Reviewers",
 				"Search reviewers",