[PhpUnitBridge] Add option `ignoreFile` to configure a file that lists …

[nicolas-grekas]

Q	A
Feature PR	symfony/symfony#45226
PR author(s)	@mondrake
Merged in	6.1

[wouterj]

Hi @mondrake, thanks for the code feature! Are you willing to write a very small doc section about this new feature? I think it would best fit under the "Configuration" section on https://symfony.com/doc/current/components/phpunit_bridge.html

[mondrake]

I tried in #16768, please review - my first doc PR