Different environments for different executors?

[TomNicholas]

Different executors have different dependencies, so we might want to run them in different CI environments.

We probably still want a single test fixture providing the runtime, but that perhaps should be parameterized at the level of different CI jobs (in a GH actions matrix).

[tomwhite]

We need different environments for different executors since the dependencies are so varied (and had conflicts in the past at least).

We could have environment-lithops-aws.yml, etc, and then create the runtime objects according to what can be imported. So for Lithops AWS we'd try to import lithops and import s3fs and if that succeeded add the corresponding config file.

Perhaps there's a more elegant way of doing it though.

[tomwhite]

Fixed in #11