fix: change serialisation test accuracy

Required for macOS python<3.11

tests/integration/test_models/standard_model_tests.py

@@ -152,15 +152,11 @@ def test_serialisation(self, solver=None, t_eval=None):
         else:
             new_solver = new_model.default_solver
 
-        if (
-            isinstance(new_model, pybamm.lithium_ion.BaseModel)
-            and new_model.options["SEI"] != "ec reaction limited (asymmetric)"
-        ):
+        if isinstance(new_model, pybamm.lithium_ion.BaseModel):
             new_solver.rtol = 1e-8
             new_solver.atol = 1e-8
-            accuracy = 6
-        else:
-            accuracy = 5
+
+        accuracy = 5
 
         Crate = abs(
             self.parameter_values["Current function [A]"]