Fix cleanup handler not called on background task expiration due to struct being captured before assignment (#115)

Author: davisg123

Sources/Segment/Plugins/Platforms/iOS/iOSLifecycleMonitor.swift

@@ -190,14 +190,15 @@ extension SegmentDestination.UploadTaskInfo {
         self.task = task
 
         if let application = UIApplication.safeShared {
-            let taskIdentifier = application.beginBackgroundTask { [self] in
-                self.task.cancel()
-                self.cleanup?()
+            var taskIdentifier: UIBackgroundTaskIdentifier = .invalid
+            taskIdentifier = application.beginBackgroundTask {
+                task.cancel()
+                application.endBackgroundTask(taskIdentifier)
             }
             self.taskID = taskIdentifier.rawValue
 
-            self.cleanup = { [self] in
-                application.endBackgroundTask(UIBackgroundTaskIdentifier(rawValue: self.taskID))
+            self.cleanup = {
+                application.endBackgroundTask(taskIdentifier)
             }
         }
     }