The Schema file is: https://github.com/aneek/rate_limiter/blob/develop/config/install/rate_limiter.settings.yml

No, that is not the schema file, that is the config file for which you need to create a configuration schema.

Tests by default enforce that your configuration has a schema, which is useful for supporting configuration translation and additional upcoming functionality like validation.

See https://www.drupal.org/docs/8/api/configuration-api/configuration-schemametadata for more information on how to create that.

The Schema file is: https://github.com/aneek/rate_limiter/blob/develop/config/install/rate_limiter.settings.yml

No, that is not the schema file, that is the config file for which you need to create a configuration schema.

Tests by default enforce that your configuration has a schema, which is useful for supporting configuration translation and additional upcoming functionality like validation.

See Configuration schema/metadata for more information on how to create that.