fix phpstan

Author: bshaffer

src/AuthHandler/Guzzle6AuthHandler.php

@@ -40,13 +40,21 @@ public function attachCredentials(
             );
         }
 
-        return $this->attachCredentialsCache($http, $credentials, $tokenCallback);
+        return $this->attachToHttp($http, $credentials, $tokenCallback);
     }
 
     public function attachCredentialsCache(
         ClientInterface $http,
         FetchAuthTokenCache $credentials,
         ?callable $tokenCallback = null
+    ) {
+        return $this->attachToHttp($http, $credentials, $tokenCallback);
+    }
+
+    private function attachToHttp(
+        ClientInterface $http,
+        FetchAuthTokenInterface $credentials,
+        ?callable $tokenCallback = null
     ) {
         // if we end up needing to make an HTTP request to retrieve credentials, we
         // can use our existing one, but we need to throw exceptions so the error
@@ -63,9 +71,7 @@ public function attachCredentialsCache(
         $config['handler']->remove('google_auth');
         $config['handler']->push($middleware, 'google_auth');
         $config['auth'] = 'google_auth';
-        $http = new Client($config);
-
-        return $http;
+        return new Client($config);
     }
 
     public function attachToken(ClientInterface $http, array $token, array $scopes)