Revert iOS SDK update in podspec

Keep only Android SDK update and test fixes. iOS SDK will remain at 18.7.3 to avoid CocoaPods dependency conflicts.

Author: prithivraj

intercom-react-native.podspec

@@ -20,5 +20,5 @@ Pod::Spec.new do |s|
   s.pod_target_xcconfig = { "DEFINES_MODULE" => "YES" }
 
   s.dependency "React-Core"
-  s.dependency "Intercom", '~> 19.1.0'
+  s.dependency "Intercom", '~> 18.7.3'
 end