refactor: add regex match for KeyError message in test

Author: Seunghan-Jung

tests/test_source_yaml.py

@@ -226,5 +226,5 @@ def settings_customise_sources(
         ) -> tuple[PydanticBaseSettingsSource, ...]:
             return (YamlConfigSettingsSource(settings_cls),)
 
-    with pytest.raises(KeyError):
+    with pytest.raises(KeyError, match=r'yaml_config_section key ".*" not found in .+'):
         Settings()