Performance improvements for pull request list page (#29900) (#29972)

This PR will avoid load pullrequest.Issue twice in pull request list
page. It will reduce x times database queries for those WIP pull
requests.

Partially fix #29585
Backport #29900

routers/web/user/notification.go

@@ -128,6 +128,12 @@ func getNotifications(ctx *context.Context) {
 		ctx.ServerError("LoadIssues", err)
 		return
 	}
+
+	if err = notifications.LoadIssuePullRequests(ctx); err != nil {
+		ctx.ServerError("LoadIssuePullRequests", err)
+		return
+	}
+
 	notifications = notifications.Without(failures)
 	failCount += len(failures)