[ios] prevent a race condition by not fulfilling the expectation until the view has been added (#5507)

platform/ios/test/MGLAnnotationViewTests.m

@@ -84,9 +84,12 @@ static NSString * const MGLTestAnnotationReuseIdentifer = @"MGLTestAnnotationReu
     
     _annotationView = annotationView;
     
-    [_expectation fulfill];
-    
     return annotationView;
 }
 
+- (void)mapView:(MGLMapView *)mapView didAddAnnotationViews:(NSArray<MGLAnnotationView *> *)annotationViews
+{
+    [_expectation fulfill];
+}
+
 @end