What is the purpose of a configuration schema file?
Drupal does not check the configuration schema at runtime when the configuration is loaded - the configuration is assumed to be correct.
The schema is used in the tests - when running tests, configurations are automatically validated against the schema to ensure they are correct. Presumably you have developed your module with tests, and by the time you make your module publicly available you will have your tests running and verifying that the configurations you are shipping are valid.
The contributed config_inspector module is very useful for validating and debugging configuration and configuration schema.