`Invalid JS responder` error was promoted to warning

Summary:
Given async nature of RN, it is quite possible situation, hence it should not be a redbox.
And in Fabric it happends all the time which makes debugging painful.

Reviewed By: mdvacca

Differential Revision: D8473511

fbshipit-source-id: cfe7a1d3d105fde3b23db4c4c07b99864215c94c

React/Modules/RCTUIManager.m

@@ -1473,7 +1473,7 @@ RCT_EXPORT_METHOD(setJSResponder:(nonnull NSNumber *)reactTag
   [self addUIBlock:^(__unused RCTUIManager *uiManager, NSDictionary<NSNumber *, UIView *> *viewRegistry) {
     _jsResponder = viewRegistry[reactTag];
     if (!_jsResponder) {
-      RCTLogError(@"Invalid view set to be the JS responder - tag %@", reactTag);
+      RCTLogWarn(@"Invalid view set to be the JS responder - tag %@", reactTag);
     }
   }];
 }