Running tests under PHPUnit 10 sometimes fails with output buffer errors (like "Test code or tested code did not close its own output buffers" and "Test code or tested code closed output buffers other than its own").

PHPUnit stops its own output buffer now before calling teardown when assertions on output are used, which makes the flush of the barrier (added in setup) to late.

Upstream related:

• https://github.com/sebastianbergmann/phpunit/commit/d5101c0d51bb2b8c608b74f12fe01b8513574d05
• https://github.com/sebastianbergmann/phpunit/commit/1bfe099511b95aa2f9284c572fb8ee0e71902ccd