Skip php-cs-fixer check on php 8 for now

[weaverryan]

The php 8 tests fails mostly because dependencies we need aren't compatible yet.

But others that might pass are failing because php-cs-fixer doesn't support php 8, so the php-cs check on the generated code fails.

To make it more clear which tests are truly failing, we should (for now) disable the php-cs-fixer check in the test for php 8. We can re-enable it later when php-cs-fixer supporst php8.

[OskarStark]

This is already fixed in #715