increase gemma3 multimodal convergence test loss atol (#697)

## Summary
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increase gemma3 multimodal convergence test loss atol
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## Details
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## Testing Done
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- [ ] run `make test` to ensure correctness
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- [ ] run `make test-convergence` to ensure convergence

Author: shivam15s

test/convergence/bf16/test_mini_models_multimodal.py

@@ -872,7 +872,7 @@ def run_mini_model_multimodal(
             32,
             1e-4,
             torch.bfloat16,
-            1e-3,
+            3e-3,
             1e-2,
             0.4,  # Increase the absolute tolerance for the logits of Gemma-3.
             1e-1,