Allow symfony/console 6.*

[ddebin]

A Symfony 6.0+ test is required because of function signatures change in Console\Application.
Maybe a better test exists instead of Runtime Composer utilities.

[oradwell]

Thanks for your PR @ddebin
what I'd do is to define it as a separate class (CoversValidatorSymfony5 and CoversValidatorSymfony6) and use class_alias. that way you don't need to put class definitions in if statements
I did something similar in FileTestCase.php#L7

I've also asked Travis-CI for more Open Source credits

[coveralls]

Coverage decreased (-7.7%) to 86.29% when pulling ed45648 on ddebin:master into 70d5d4b on oradwell:master.

[oradwell]

merged in #41