4.5 WebTestCase $environment BC break

[mikysan]

Preconditions

1. PHP 8.0
2. Symfony 5.4
3. liip/functional-test-bundle 4.5

Steps to reproduce

1. rename Symfony test environment to testing
2. create a test like following

   
   namespace App\Tests;

use Liip\FunctionalTestBundle\Test\WebTestCase;

class FunctionalTestCase extends WebTestCase { protected $environment = 'testing';

public function testFoo()
{
    $this->assertTrue(true);
}

}

### Expected result
The test should pass or at least should be failing with a proper error message or deprecation warning

### Actual result
test fail with `You have requested a non-existent parameter "secret".` error message.