Address review comments: use actorDisplayName for Copilot author display

- Add actorDisplayName call in CommentAuthor.DisplayName for consistency
- Use require.Equal in TestActorDisplayName instead of manual comparisons
- Simplify user type name constant usage

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

api/queries_pr_review.go

@@ -143,6 +143,7 @@ type RequestedReviewer struct {
 
 const teamTypeName = "Team"
 const botTypeName = "Bot"
+const userTypeName = "User"
 
 func (r RequestedReviewer) LoginOrSlug() string {
 	if r.TypeName == teamTypeName {

api/queries_repo.go

@@ -1135,7 +1135,7 @@ func NewAssignableUser(id, login, name string) AssignableUser {
 
 // DisplayName returns a user-friendly name via actorDisplayName.
 func (u AssignableUser) DisplayName() string {
-	return actorDisplayName("User", u.login, u.name)
+	return actorDisplayName(userTypeName, u.login, u.name)
 }
 
 func (u AssignableUser) ID() string {
@@ -1165,7 +1165,7 @@ func NewAssignableBot(id, login string) AssignableBot {
 }
 
 func (b AssignableBot) DisplayName() string {
-	return actorDisplayName("Bot", b.login, "")
+	return actorDisplayName(botTypeName, b.login, "")
 }
 
 func (b AssignableBot) ID() string {

api/queries_repo_test.go

@@ -583,10 +583,7 @@ func TestActorDisplayName(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got := actorDisplayName(tt.typeName, tt.login, tt.actName)
-			if got != tt.want {
-				t.Errorf("actorDisplayName(%q, %q, %q) = %q, want %q", tt.typeName, tt.login, tt.actName, got, tt.want)
-			}
+			require.Equal(t, tt.want, actorDisplayName(tt.typeName, tt.login, tt.actName))
 		})
 	}
 }