Symfony version(s) affected: 4.4.8

Description
Working with Symfony 4.4.8 and PHP 7.4.5, having thoses errors after upgrading symfony/phpunit-bridge to 5.1.0 :

• Notice: Undefined index: versions in /var/www/html/vendor/symfony/phpunit-bridge/bin/simple-phpunit.php on line 185
• Warning: count(): Parameter must be an array or an object that implements Countable in /var/www/html/vendor/symfony/phpunit-bridge/bin/simple-phpunit.php on line 185
• sh: 1: composer: not found

How to reproduce

1. Install PHP 7.4.5
2. Install Symfony 4.4.8
3. Install phpunit-bridge 5.1.0
4. Run bin/phpunit

Possible Solution

Additional context

Works fine with only downgrading phpunit-bridge to 5.0.8

• Composer version 1.10.5