Fix istropic_pec checking

tidy3d/components/medium.py

@@ -784,7 +784,7 @@ def sigma_model(self, freq: float) -> complex:
     @cached_property
     def is_isotropic_pec(self):
         """Whether all components are PEC."""
-        return any(self.is_comp_pec(i) for i in range(3))
+        return all(self.is_comp_pec(i) for i in range(3))
 
     def is_comp_pec(self, comp: Axis):
         """Whether the component is a PEC."""