[auth] Address Xcode 16.2 concurrency compile time issues (#14279)

Author: paulb777

FirebaseAuth/CHANGELOG.md

@@ -2,6 +2,7 @@
 - [fixed] Fix Multi-factor session crash on second Firebase app. (#14238)
 - [fixed] Updated most decoders to be consistent with Firebase 10's behavior
   for decoding `nil` values. (#14212)
+- [fixed] Address Xcode 16.2 concurrency compile time issues. (#14279)
 
 # 11.6.0
 - [added] Added reCAPTCHA Enterprise support for app verification during phone

FirebaseAuth/Sources/Swift/Auth/Auth.swift

@@ -144,6 +144,7 @@ extension Auth: AuthInterop {
 ///
 /// This class is thread-safe.
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
+@preconcurrency
 @objc(FIRAuth) open class Auth: NSObject {
   /// Gets the auth object for the default Firebase app.
   ///

FirebaseAuth/Sources/Swift/SystemService/AuthNotificationManager.swift

@@ -18,6 +18,7 @@
 
   /// A class represents a credential that proves the identity of the app.
   @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
+  @preconcurrency
   class AuthNotificationManager {
     /// The key to locate payload data in the remote notification.
     private let kNotificationDataKey = "com.google.firebase.auth"