Symfony version(s) affected: Since 3.4.0 it seems ?

Description
If you have let's say composer 1 and composer 2 both installed with different binary paths, you before had the possibility to tell phpunit-bridge what executable it should use.

This is not the case anymore, so it will always fallback (or try to find) a composer binary... which can be 1.0, when there can be another binary such as composer2 available.

How to reproduce
Install both versions of composer, let's say composer and composer2. composer will always be used, even if you set the COMPOSER_BINARY variable as it should be.

Possible Solution
Reintroduce the COMPOSER_BINARY env var in the simple-phpunit bridge since 4.4.