fix(deps): update dependency firebase_auth to v6

Author: renovate[bot]

pubspec.yaml

@@ -14,7 +14,7 @@ dependencies:
 
   # Firebase
   firebase_core: ^3.4.0
-  firebase_auth: ^5.2.0
+  firebase_auth: 6.1.1
   firebase_auth_platform_interface: ^7.0.0
 
   # Firebase Authentications