Symfony version(s) affected: >= 3.4

Description
the FilesystemTestCase has the same issue that #30071

How to reproduce
Run a test extending FilesystemTestCase with PHPUnit 8 will produce:
PHP Fatal error: Declaration of Symfony\Component\Filesystem\Tests\FilesystemTestCase::setUpBeforeClass() must be compatible with PHPUnit\Framework\TestCase::setUpBeforeClass(): void

Possible Solution
Use the same solution that #30474