Fix import bug (#9624)

* Fix import bug

* add test

* make test better

Author: morganchen12

FirebaseAuth/CHANGELOG.md

@@ -1,3 +1,6 @@
+# v9.0.0
+- [fixed] **Breaking change:** Fixed an ObjC-to-Swift API conversion error where `getStoredUser(forAccessGroup:)` returned a non-optional type. This change is breaking for Swift users only (#8599).
+
 # v8.14.0
 - [added] Started to collect the Firebase user agent for Firebase Auth. (#9066)
 

FirebaseAuth/Sources/Public/FirebaseAuth/FIRAuth.h

@@ -866,7 +866,8 @@ NS_SWIFT_NAME(Auth)
         Please refer to https://github.com/firebase/firebase-ios-sdk/issues/8878 for details.
  */
 - (nullable FIRUser *)getStoredUserForAccessGroup:(NSString *_Nullable)accessGroup
-                                            error:(NSError *_Nullable *_Nullable)outError;
+                                            error:(NSError *_Nullable *_Nullable)outError
+    __attribute__((swift_error(nonnull_error)));  // This method can return `nil` on success.
 
 @end
 

FirebaseAuth/Tests/Sample/SwiftApiTests/SwiftAPI.swift

@@ -87,7 +87,13 @@ class AuthAPI_hOnlyTests: XCTestCase {
     auth.setAPNSToken(Data(), type: AuthAPNSTokenType(rawValue: 2)!)
     auth.canHandleNotification([:])
     try auth.useUserAccessGroup("abc")
-    try auth.getStoredUser(forAccessGroup: "def")
+    let nilUser = try auth.getStoredUser(forAccessGroup: "def")
+    // If nilUser is not optional, this will raise a compiler error.
+    // This condition does not need to execute, and may not if prior
+    // functions throw.
+    if let value = nilUser {
+      XCTAssert(true)
+    }
   }
 
   #if compiler(>=5.5.2) && canImport(_Concurrency)