Module lint: Fail instead of warn if local copy edited

[ewels]

If the local copy of a module is edited and does not match the remote, throw an error instead of a warning (with a clearer message too).

Fixes #1313

Not sure if there are cases where we don't want this to happen? But I can't think of any.

PR checklist

• This comment contains a description of changes (with reason)
• CHANGELOG.md is updated
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

[ewels]

CI failing because we are now picking up the fact that the pytests edit files in place for the purposes of testing 🤦🏻‍♂️

[JoseEspinosa]

LGTM! 🚀