Raise atol in MobileNetV3 unit tests

MobileNetV3 was sporadically failing with the previously set absolute
difference threshold. Raise it to prevent flaky test status.

Change-Id: I78d4336c3bf96902ee8b4536391c45f8a97b6533

Author: Martin Lindström

backends/arm/test/models/test_mobilenet_v3_arm.py

@@ -46,7 +46,7 @@ def test_mv3_tosa_BI():
         aten_op=[],
         exir_op=[],
         use_to_edge_transform_and_lower=True,
-        atol=0.3,
+        atol=0.5,
         qtol=1,
     )
     pipeline.run()
@@ -63,7 +63,7 @@ def test_mv3_u55_BI():
         exir_ops=[],
         run_on_fvp=True,
         use_to_edge_transform_and_lower=True,
-        atol=0.3,
+        atol=0.5,
         qtol=1,
     )
     pipeline.run()
@@ -80,7 +80,7 @@ def test_mv3_u85_BI():
         exir_ops=[],
         run_on_fvp=True,
         use_to_edge_transform_and_lower=True,
-        atol=0.3,
+        atol=0.5,
         qtol=1,
     )
     pipeline.run()