Fixed typo in PHPUnit test code. #2867

[websuke]

Fixes were made so that the test would pass.
Thank you for your confirmation.

[kylekatarnls]

Right now this test pass on both Windows and Linux on all PHP versions in GitHub Actions:
https://github.com/briannesbitt/Carbon/actions/runs/6486348590

(It's using PHPStan 1.10.38 as of now)

It also pass locally in my env.

So I would expect jobs to fail if we merge that.

You might have something different in your env.

[websuke]

@kylekatarnls
I have confirmed that it works on both my Mac and Ubuntu by modifying it, but the environment may be bad in both. We will close it. I apologize for the trouble.