Fix Muon unit tests for reduce_scatter incompatibility assertion

[Copilot]

Unit tests for Muon optimizer fail after PR deepspeedai#7808 added assertion that Muon is incompatible with reduce_scatter=True. Tests were using the default reduce_scatter=True value.

Changes

tests/unit/ops/muon/test_muon.py

• Set reduce_scatter=False for Muon optimizer tests, keep True for Adam tests
• Add TestMuonReduceScatterIncompatibility to verify assertion triggers correctly

config_dict = {
    "zero_optimization": {
        "stage": zero_stage,
        "reduce_scatter": False if optimizer_type == "muon" else True,
    }
}

The new test verifies that initializing Muon with reduce_scatter=True raises AssertionError with message "incompatible with Muon optimizer".

Original prompt

The newly created branch "fix_unit_tests" in repository "nathon-lee/DeepSpeed_woo" is based on the branch fix_issue_7807. It aims to address the unit test failures observed in pull request "deepspeedai#7808". The specific failure logs and error messages are associated with this PR (available at: deepspeedai#7808) and may provide detailed context about the issues at hand.

Objective:

• Investigate the unit test failure logs provided in fix: Ensure full gradient reduction for Muon with reduce_scatter deepspeedai/DeepSpeed#7808.
• Identify the root causes of the unit test failures.
• Implement appropriate fixes to resolve the issues, ensuring all unit tests pass.
• Test the changes thoroughly to confirm the fixes are effective.

Let me know if additional information is needed before starting.

This pull request was created from Copilot chat.

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