Use Top materializations for TypeIs special form

Author: AlexWaygood

crates/ty_python_semantic/src/types/infer/builder/type_expression.rs

@@ -1286,7 +1286,11 @@ impl<'db> TypeInferenceBuilder<'db, '_> {
 
                     Type::unknown()
                 }
-                _ => TypeIsType::unbound(self.db(), self.infer_type_expression(arguments_slice)),
+                _ => TypeIsType::unbound(
+                    self.db(),
+                    self.infer_type_expression(arguments_slice)
+                        .top_materialization(self.db()),
+                ),
             },
             SpecialFormType::TypeGuard => {
                 self.infer_type_expression(arguments_slice);