Symfony version(s) affected: all

Description
The phpunit bridge sets the COMPOSER_ROOT_VERSION to 6.5.99 (.e.g) and will then install dev versions as well - and not stable versions.

How to reproduce
delete vendor/bin/.phpunit and use simple-phpunit again. It will install the latest commit in phpunit repo (e.g. branch 6.5)

Possible Solution
I'm not 100% sure: use prefer-stable: true and minimium-compability: stable in the composer.json from phpunit?

Thank you

Best regards
Philipp