Remove trailing slash from source filter in event subscription.

src/Altinn.App.Core/Infrastructure/Clients/Events/EventsSubscriptionClient.cs

@@ -57,7 +57,7 @@ public async Task<Subscription> AddSubscription(string org, string app, string e
             {
                 TypeFilter = eventType,
                 EndPoint = new Uri($"{appBaseUrl}api/v1/eventsreceiver?code={await _secretCodeProvider.GetSecretCode()}"),
-                SourceFilter = new Uri(appBaseUrl)
+                SourceFilter = new Uri(appBaseUrl.TrimEnd('/')) // The event system is requireing the source filter to be without trailing slash
             };
 
             string serializedSubscriptionRequest = JsonSerializer.Serialize(subscriptionRequest);