[IOS] The onMessageReceivedInTheForeground callback triggers multiple times for a single notification

[ebabhi]

Issue

When the app is in the foreground and receives a notification, the onMessageReceivedInTheForeground callback is triggered multiple times.

Expected Behaviour

onMessageReceivedInTheForeground should only be triggered once per notification.

Steps to replicate

1. Set up Pusher Beams on iOS.
2. Add a callback to onMessageReceivedInTheForeground.
3. The callback will be triggered multiple times.

Logs from Xcode for a single notification

SwiftPusherBeamsPlugin: message received: ["body": "DEBUG", "data": Optional({
    pusher =     {
        instanceId = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx";
        publishId = "pubid-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx";
        userShouldIgnore = 1;
    };
}), "title": "DEBUG"]
flutter: {pusher: {userShouldIgnore: true, publishId: pubid-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, instanceId: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}}
SwiftPusherBeamsPlugin: message received: ["body": "DEBUG", "data": nil, "title": "DEBUG"]
SwiftPusherBeamsPlugin: message received: ["body": "DEBUG", "data": Optional({
    pusher =     {
        instanceId = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx";
        publishId = "pubid-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx";
        userShouldIgnore = 1;
    };
}), "title": "DEBUG"]
flutter: null
flutter: {pusher: {userShouldIgnore: true, publishId: pubid-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, instanceId: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}}
SwiftPusherBeamsPlugin: message received: ["body": "DEBUG", "data": nil, "title": "DEBUG"]
SwiftPusherBeamsPlugin: message received: ["body": "DEBUG", "data": nil, "title": "DEBUG"]
flutter: null
flutter: null
SwiftPusherBeamsPlugin: message received: ["body": "DEBUG", "data": nil, "title": "DEBUG"]
flutter: null