Fix issue will be detected as pull request when checking `First-time contributor` (#28237)

Fix #28224

routers/web/repo/issue.go

@@ -1319,7 +1319,7 @@ func roleDescriptor(ctx stdCtx.Context, repo *repo_model.Repository, poster *use
 		return roleDescriptor, err
 	} else if hasMergedPR {
 		roleDescriptor.RoleInRepo = issues_model.RoleRepoContributor
-	} else {
+	} else if issue.IsPull {
 		// only display first time contributor in the first opening pull request
 		roleDescriptor.RoleInRepo = issues_model.RoleRepoFirstTimeContributor
 	}