Fix "Supertypes through typealias cannot be nullable. This will become an error in language version 2.3."

Author: BoD

libraries/apollo-runtime/src/appleMain/kotlin/com/apollographql/apollo/network/NetworkObserver.apple.kt

@@ -7,12 +7,11 @@ import platform.Network.nw_path_monitor_set_queue
 import platform.Network.nw_path_monitor_set_update_handler
 import platform.Network.nw_path_monitor_start
 import platform.Network.nw_path_monitor_t
-import platform.Network.nw_path_monitor_update_handler_t
 import platform.Network.nw_path_status_satisfied
 import platform.Network.nw_path_t
 import platform.darwin.dispatch_queue_create
 
-internal class AppleNetworkObserver: NetworkObserver, nw_path_monitor_update_handler_t {
+internal class AppleNetworkObserver: NetworkObserver, ((nw_path_t) -> Unit) {
   var monitor: nw_path_monitor_t = null
   var listener: NetworkObserver.Listener? = null
 
@@ -36,4 +35,4 @@ internal class AppleNetworkObserver: NetworkObserver, nw_path_monitor_update_han
   override fun invoke(p1: nw_path_t) {
     listener?.networkChanged((nw_path_get_status(p1) == nw_path_status_satisfied))
   }
-}
+}