Enable complete_nullability on //xplat/js/react-native-github:RCTTypeSafety (#32473)

Summary: Pull Request resolved: https://github.com/facebook/react-native/pull/32473

Reviewed By: AdamCmiel

Differential Revision: D31775069

fbshipit-source-id: f3aaee36c1ca8a209610f8b66c7adc90bd2b8c7e

BUCK

@@ -549,6 +549,7 @@ rn_apple_library(
         ],
     ),
     autoglob = False,
+    complete_nullability = True,
     contacts = ["oncall+react_native@xmail.facebook.com"],
     extension_api_only = True,
     frameworks = [