Fix a test error in gson/extra

[thaibui]

GraphAdapterBuilderTest fails on master when execute mvn -e clean test under json/extras directory; this PR should fix the issue.

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[thaibui]

I signed it!

[googlebot]

CLAs look good, thanks!

[swankjesse]

This test case used to pass, but it was regressed with this change:
8d5a413

@inder123 thoughts on self-references?

[Marcono1234]

Probably obsolete now due to #1959 (comment).

Though at least personally I think it might be worth revisiting the self-reference detection of ReflectiveTypeAdapterFactory again at some point. It only detects direct self-references so this only helps for a very specific case. Additionally, if this was only done to support serialization of Throwable, then removing the direct self-reference check would not be so problematic because you should not serialize JDK classes using reflection.

[eamonnmcmanus]

Closing as obsolete. If we do want to revisit the self-reference detection of ReflectiveTypeAdapterFactory then that should be a separate issue.