Should we use mock server in test?

I got these errors while running tests via PHPUnit locally.

```
2) ReferenceTest::testResolveFileHttp
cebe\openapi\exceptions\UnresolvableReferenceException: Failed to resolve Reference 'definitions.yaml#/Pet' to cebe\openapi\spec\Schema Object: file_get_contents(https://raw.githubusercontent.com/cebe/php-openapi/290389bbd337cf4d70ecedfd3a3d886715e19552/tests/spec/data/reference/definitions.yaml): failed to open stream: HTTP request failed! HTTP/1.1 429 Too Many Requests

/app/src/spec/Reference.php:226
/app/src/SpecBaseObject.php:416
/app/src/SpecBaseObject.php:412
/app/tests/spec/ReferenceTest.php:247
phpvfscomposer:///app/vendor/phpunit/phpunit/phpunit:106

Caused by
PHPUnit\Framework\Error\Warning: file_get_contents(https://raw.githubusercontent.com/cebe/php-openapi/290389bbd337cf4d70ecedfd3a3d886715e19552/tests/spec/data/reference/definitions.yaml): failed to open stream: HTTP request failed! HTTP/1.1 429 Too Many Requests

/app/src/ReferenceContext.php:217
/app/src/spec/Reference.php:224
/app/src/SpecBaseObject.php:416
/app/src/SpecBaseObject.php:412
/app/tests/spec/ReferenceTest.php:247
phpvfscomposer:///app/vendor/phpunit/phpunit/phpunit:106

```

Should we use mock server to fix this issue?

Commencez par tests/spec/ReferenceTest.php, en particulier testResolveFileHttp, et suivez l’échec à travers src/spec/Reference.php et src/ReferenceContext.php. Déterminez comment le fixture peut éviter les limites de débit de raw.githubusercontent.com, puis exécutez le test PHPUnit pour vérifier qu’il ne dépend plus de cette requête externe.

Rédigé par le modèle d'indexation à partir du texte de l'issue.