Unable to create `merge_queue` rule

[stegayet]

merge_queue rule cannot be created as it is being shown the following error:

  | Error: POST https://api.github.com/repos/gh-terraform-provider-tester/tf-acc-test-merge-queue-wdu19/rulesets: 422 Validation Failed [{Resource: Field: Code: Message:Invalid rule 'merge_queue': }]

I'll investigate later on

Originally posted by @stegayet in #13 (comment)