ci(ios): disable Flipper to improve build times (#1194)

Author: tido64

example/ios/Podfile

@@ -2,7 +2,7 @@ require_relative '../node_modules/react-native-test-app/test_app'
 
 workspace 'Example.xcworkspace'
 
-use_flipper! false if ENV['DISABLE_FLIPPER']
+use_flipper! false unless ENV['ENABLE_FLIPPER']
 
 options = {
   :fabric_enabled => false,