[Auth] Add objc attribute to UserInfoImpl so legacy decoding works (#14169)

Author: ncooke3

FirebaseAuth/CHANGELOG.md

@@ -2,6 +2,8 @@
 - [fixed] Restore Firebase 10 behavior by synchronizing access to the
   `Auth.currentUser` API. This resolves some Firebase 11 issues where the
   current user is unexpectedly `nil` at startup.
+- [fixed] Restore Firebase 10 decoding behavior to prevent user provider data
+  from being decoded as `nil`. (#14011)
 
 # 11.5.0
 - [fixed] Restore pre-Firebase 11 decoding behavior to prevent users getting

FirebaseAuth/Sources/Swift/User/UserInfoImpl.swift

@@ -18,6 +18,7 @@ import Foundation
 extension UserInfoImpl: NSSecureCoding {}
 
 @available(iOS 13, tvOS 13, macOS 10.15, macCatalyst 13, watchOS 7, *)
+@objc(FIRUserInfoImpl) // objc Needed for decoding old versions
 class UserInfoImpl: NSObject, UserInfo {
   /// A convenience factory method for constructing a `UserInfo` instance from data
   /// returned by the getAccountInfo endpoint.