[Auth] nil out SafariViewController when presentation finishes (#13715)

Author: ncooke3

FirebaseAuth/CHANGELOG.md

@@ -5,6 +5,8 @@
 - [Fixed] Prevent a bad memory access crash by using non-ObjC, native Swift
   types in the SDK's networking layer, and moving synchronous work off of
   the shared Swift concurrency queue. (#13650)
+- [Fixed] Restore Firebase 10 behavior by forwarding errors from interrupted
+  reCAPTCHA or OIDC login flows. (#13645)
 
 # 11.2.0
 - [Fixed] Fixed crashes that could occur in Swift continuation blocks running in the Xcode 16

FirebaseAuth/Sources/Swift/Utilities/AuthURLPresenter.swift

@@ -89,6 +89,7 @@
     func safariViewControllerDidFinish(_ controller: SFSafariViewController) {
       kAuthGlobalWorkQueue.async {
         if controller == self.safariViewController {
+          self.safariViewController = nil
           // TODO: Ensure that the SFSafariViewController is actually removed from the screen
           // before invoking finishPresentation
           self.finishPresentation(withURL: nil,