Add Gemma3 GQA fusion test case

[gramalingam]

Add Gemma3 GQA fusion test case: variant with SimplifiedLayerNormalization applied to query and key.

[codecov]

Codecov Report

❌ Patch coverage is 51.58730% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.32%. Comparing base (55f5b82) to head (f1053ea).
⚠️ 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	51.58%	61 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2642      +/-   ##
==========================================
- Coverage   70.35%   70.32%   -0.04%     
==========================================
  Files         222      222              
  Lines       26312    26438     +126     
  Branches     2632     2632              
==========================================
+ Hits        18513    18593      +80     
- Misses       6877     6926      +49     
+ Partials      922      919       -3     

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