Remove the default value for the test_suffix parameter (#64)

Passing a comma-separated list of values to the CLI argument
--test-suffix has been deprecated in PHPUnit 11[1] and will no longer
work in PHPUnit 12.  Given that this action is sending its default
value[2] anyways, there's no reason to explicitly provide this command
line argument.  Further, it's confusing that this command line argument
is specified at all when nothing in my repo's configuration sets its
value.

[1]: sebastianbergmann/phpunit#5709
[2]: https://docs.phpunit.de/en/11.1/textui.html#selection

Coverage options (#52)

* docs: add missing config options

* feature: implement coverage options

* wip: equals required for optional arg

* wip: bump hash

* wip: typo

February 2023

feature: force colours in cli

feature: silent download

Group output on error (#32)

Pass all environment variables into subcontainer

Merge branch '17-php-versions'