backport correction tests

tests/TestCase/Auth/Authenticator/KeycloakAuthenticatorTest.php

@@ -36,8 +36,15 @@ class KeycloakAuthenticatorTest extends TestCase
         $json = json_encode(['preferred_username' => 'testunit', 'access_token' => 'test']); // user.1
         $response = $this->createMock(Client\Response::class);
         $response->method('getStringBody')->willReturn($json);
-        $client = $this->createMock(Client::class);
-        $client->method('post')->willReturn($response);
+        $client = new class extends Client {
+            public static Client\Response $response;
+            // phpcs:ignore
+            public function post(string $url, $data = [], array $options = []): Client\Response
+            {
+                return self::$response;
+            }
+        };
+        $client::$response = $response;
         Utility::set(Client::class, $client);
 
         $identity = new KeycloakIdentifier(['access_token' => 'test']);