Describe the bug

⇒  gh --version
gh version 1.8.0 (2021-03-30)
https://github.com/cli/cli/releases/tag/v1.8.0

Steps to reproduce the behavior

If you try to gh pr merge --auto on a repository that doesn't have auto merge enabled, the tool will still tell you that the PR will be merged once all checks have passed.

Expected vs actual behavior

I would expect the cli to tell me that it can't auto merge the PR since auto merging is not enabled on this PR.