Ensure gov banner defined before use

GitOrigin-RevId: 1db97fd4882600f8e6764273bbcbec503b68f01e

services/web/frontend/js/features/project-list/components/notifications/user-notifications.tsx

@@ -80,7 +80,7 @@ function UserNotifications() {
         <ReconfirmationInfo />
         <GeoBanners />
         {!showWritefull && !dismissedWritefull && <GroupsAndEnterpriseBanner />}
-        <USGovBanner />
+        {USGovBanner && <USGovBanner />}
 
         <AccessibilitySurveyBanner />