Cortex-M: Use default atol for ResNet8 dialect test

The dialect test was using atol=0.1 while the implementation test used
the default atol=1e-03, which is backwards — the CPU graph comparison
should not need a looser tolerance than hardware simulation. Remove the
override; the test passes at the stricter default.

Co-authored-by: Claude <noreply@anthropic.com>

Author: rascani

backends/cortex_m/test/models/test_resnet8.py

@@ -45,7 +45,7 @@
 def test_dialect_resnet8(test_case):
     inputs = test_case.get_example_inputs()
     tester = CortexMTester(test_case.model, inputs)
-    tester.test_dialect(ops_before_transforms, ops_after_transforms, qtol=1, atol=0.1)
+    tester.test_dialect(ops_before_transforms, ops_after_transforms, qtol=1)
 
 
 @parametrize("test_case", test_cases)