Arm backend: Update epsilon to correct default of 2**-12 (#16096)

### Summary
Epsilon was set too high in the test pipeline. Fix this to be the
correct default of: 2**-12

Signed-off-by: Saoirse Stewart <saoirse.stewart@arm.com>

Author: SaoirseARM

backends/arm/test/tester/test_pipeline.py

@@ -376,7 +376,7 @@ def __init__(
         qtol: int = 1,
         dynamic_shapes: Optional[Tuple[Any]] = None,
         tosa_extensions: Optional[List[str]] = None,
-        epsilon: float = 2**12,
+        epsilon: float = 2**-12,
     ):
         if tosa_extensions is None:
             tosa_extensions = []
@@ -570,7 +570,7 @@ def __init__(
         atol: float = 1e-03,
         rtol: float = 1e-03,
         qtol: int = 1,
-        epsilon: float = 2**12,
+        epsilon: float = 2**-12,
     ):
         compile_spec = common.get_u55_compile_spec(
             custom_path=custom_path,
@@ -671,7 +671,7 @@ def __init__(
         atol: float = 1e-03,
         rtol: float = 1e-03,
         qtol: int = 1,
-        epsilon: float = 2**12,
+        epsilon: float = 2**-12,
     ):
         compile_spec = common.get_u85_compile_spec(
             custom_path=custom_path,