[JAX] Move parallel encoder tests to L0 distributed test set.

[phu0ngng]

Description

test_multigpu_encoder.py, test_multiprocessing_encoder.py, and test_model_parallel_encoder.py belonged to the L0 test set thus were always executed on a single GPU node in the CI.

This PR moved those tests into the L0 distributed test set.

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• 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)
• Infra/Build change
• Code refractor

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• 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

[ksivaman]

LGTM

[phu0ngng]

Pipeline #129367567.