Fix qwen2 config

[RdoubleA]

Context

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7B_full_single_device uses both optimizer in bwd and grad accum, which is not compatible. Just turn off grad accum.

Changelog

What are the changes made in this PR?
*

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[pytorch-bot]

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 26.79%. Comparing base (6b55c1d) to head (c6cdc69).
Report is 16 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1620       +/-   ##
===========================================
- Coverage   72.27%   26.79%   -45.48%     
===========================================
  Files         290      290               
  Lines       14552    14556        +4     
===========================================
- Hits        10517     3901     -6616     
- Misses       4035    10655     +6620     

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