fix for _userAccessGroup being nil when getStoredUserForAccessGroup is called (#7472)

* shareLoginAcrossDevices

* shareLoginAcrossDevices

* shareLoginAcrossDevices

* shareLoginAcrossDevices

* formatting

* feedback changes

* linted

* setting _userAccessGroup needs to happen before getStoredUserForAccessGroup is called, because otherwise on first app launch, _userAccessGroup will be null, making it impossible for the app to find the shared keychain

* proper fix as suggested by rosalyntan

Author: joehinkle11

FirebaseAuth/Sources/Auth/FIRAuth.m

@@ -2258,7 +2258,7 @@ - (nullable FIRUser *)getStoredUserForAccessGroup:(NSString *_Nullable)accessGro
 #endif  // TARGET_OS_WATCH
     user = [unarchiver decodeObjectOfClass:[FIRUser class] forKey:userKey];
   } else {
-    user = [self.storedUserManager getStoredUserForAccessGroup:self.userAccessGroup
+    user = [self.storedUserManager getStoredUserForAccessGroup:accessGroup
                                    shareAuthStateAcrossDevices:self.shareAuthStateAcrossDevices
                                              projectIdentifier:self.app.options.APIKey
                                                          error:outError];