test: modify test to verify behavior of empty response exception

Author: Vinzent03

packages/gotrue/test/client_test.dart

@@ -484,8 +484,11 @@ void main() {
       try {
         await client.signInWithPassword(email: email1, password: password);
       } catch (error) {
-        expect(error, isA<AuthException>());
-        expect((error as AuthException).statusCode, '420');
+        expect(error, isA<AuthUnknownException>());
+        error as AuthUnknownException;
+        expect(error.statusCode, '420');
+        expect(error.originalError, isA<http.Response>());
+        expect(error.message, contains('empty response'));
       }
     });
   });

packages/gotrue/test/custom_http_client.dart

@@ -10,7 +10,7 @@ class CustomHttpClient extends BaseClient {
   Future<StreamedResponse> send(BaseRequest request) async {
     //Return custom status code to check for usage of this client.
     return StreamedResponse(
-      request.finalize(),
+      Stream.empty(),
       420,
       request: request,
     );