Use multiprocessing.get_all_start_methods() in test_async_with_dynamically_registered_env

[traversaro]

Description

On Windows, I was obtaining these test failures:

2024-10-20T14:32:51.8042643Z FAILED tests/envs/registration/test_make_vec.py::test_async_with_dynamically_registered_env[fork] - ValueError: cannot find context for 'fork'
2024-10-20T14:32:51.8043645Z FAILED tests/envs/registration/test_make_vec.py::test_async_with_dynamically_registered_env[forkserver] - ValueError: cannot find context for 'forkserver'

This is happening as fork and forkserver are not supported on Windows, and other platforms may have similar limitations. To avoid such test failures, I modified the test_async_with_dynamically_registered_env parametrization to use multiprocessing.get_all_start_methods() instead of hardcoding ["spawn", "fork", "forkserver"] on all platforms.

Type of change

Please delete options that are not relevant.

• Documentation only change (no code changed)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Screenshots

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Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[traversaro]

Ah, sorry for typo and thanks for the fast review!