Add GQA fusion test cases

[gramalingam]

Add GQA fusion test cases to cover extensions introduced recently to cover patterns seen in Qwen.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.43%. Comparing base (3846705) to head (70b5298).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
onnxscript/rewriter/ort_fusions/gqa_test.py	33.33%	14 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2669      +/-   ##
==========================================
- Coverage   70.45%   70.43%   -0.02%     
==========================================
  Files         224      224              
  Lines       26751    26765      +14     
  Branches     2678     2680       +2     
==========================================
+ Hits        18847    18853       +6     
- Misses       6973     6981       +8     
  Partials      931      931              

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