[Auth] Fix 'PhoneAuthProviderFake.swift' following Swift 6 changes (#14895)

Author: ncooke3

.github/workflows/combine.yml

@@ -33,12 +33,13 @@ on:
  # Rebuild on Ruby infrastructure changes.
  - 'Gemfile'
 
- # Dependencies (Disabled to avoid building Firestore in presubmits)
- # - 'FirebaseCore/**'
- # - 'FirebaseAuth/**'
- # - 'FirebaseFunctions/**'
- # - 'Firestore/**'
- # - 'FirebaseStorage/**'
+ # Dependencies
+ - 'FirebaseCore/**'
+ - 'FirebaseTestingSupport/**'
+ - 'FirebaseAuth/**'
+ - 'FirebaseFunctions/**'
+ - 'FirebaseStorage/**'
+ # - 'Firestore/**' # (Disabled to avoid building Firestore in presubmits)
 
  schedule:
  # Run every day at 11pm (PST) - cron uses UTC times

FirebaseTestingSupport/Auth/Sources/PhoneAuthProviderFake.swift

@@ -16,16 +16,16 @@
 import Foundation
 
 /// A fake object to replace a real `AuthAPNSTokenManager` in tests.
-public class PhoneAuthProviderFake: PhoneAuthProvider {
+public class PhoneAuthProviderFake: PhoneAuthProvider, @unchecked Sendable {
  override init(auth: Auth) {
  super.init(auth: auth)
  }
 
- var verifyPhoneNumberHandler: (((String?, Error?) -> Void) -> Void)?
+ var verifyPhoneNumberHandler: ((@MainActor (String?, Error?) -> Void) -> Void)?
 
  override public func verifyPhoneNumber(_ phoneNumber: String,
  uiDelegate: AuthUIDelegate? = nil,
- completion: ((_: String?, _: Error?) -> Void)?) {
+ completion: (@MainActor (String?, Error?) -> Void)?) {
  if let verifyPhoneNumberHandler,
  let completion {
  verifyPhoneNumberHandler(completion)