[Sessions] Fix test app crash

Author: ncooke3

FirebaseSessions/Tests/TestApp/Shared/AppQualityDevAppApp.swift

@@ -18,8 +18,8 @@ import FirebaseSessions
 import SwiftUI
 
 @main
-class AppQualityDevAppApp: App {
-  required init() {
+struct AppQualityDevAppApp: App {
+  init() {
     // In other Product SDKs, this is called via `+ load`, but
     // we're faking that here because Swift doesn't have `+ load`
     MockSubscriberSDK.addDependency()