test(toml): fix path assertion in arbitrary type test

Author: zigai

tests/test_confdantic.py

@@ -217,7 +217,7 @@ class ArbitraryTomlModel(Confdantic):
 
     model.save(str(filepath), comments=False, serialize_unsupported=True)
     content = filepath.read_text()
-    expected_path = base_path.as_posix()
+    expected_path = str(base_path)
     assert f'base_path = "{expected_path}"' in content