Added Atari environments to tests, removed dead code

[Markus28]

• Adds some atari environments to tested environments (if gym and ale are available)
• Removed definition of minimum_testing_env_specs, which was dead code, also didn't make sense (compared specs to strings, I think)
• Atari environments are currently not being tested for render_mode because GymEnvironment doesn't support that kwarg

Tests are currently not passing locally, which seems to be due to an unrelated problem

[pseudo-rnd-thoughts]

Looks good to me, could you just add a comment before the atari_id to explain why though particular environments were selected.
We could replace the list with all of the environment ids in the registry that contains "Pong" just in case the number of environment expands

[Markus28]

Yeah, I will add that comment :)

I also considered fetching the ids from the (old) Gym registry, but I decided against it because that registry should not really change, given that Gym is no longer being maintained. Also, I would be somewhat worried that for some reason (e.g. ale not being installed) no Atari envs show up in the registry and the test is silently skipped.

Currently, neither this test, nor test_gym_conversion are in CI, because gym isn't being installed.