chore: imports

Author: MichaelVerdon

packages/firebase_messaging/firebase_messaging/ios/firebase_messaging/Sources/firebase_messaging/include/FLTFirebaseMessagingPlugin.h

@@ -14,7 +14,7 @@
 #import <Foundation/Foundation.h>
 #import <UserNotifications/UserNotifications.h>
 
-#if __has_include(<firebase_core_shared/firebase_core_shared-Swift.h>)
+#ifdef SWIFT_PACKAGE
 @import firebase_core_shared;
 #else
 @import firebase_core;