Support fine-grained PATs

**Description**

Fine-grained PATs cause an error saying `read:org` is missing, even though the PAT has read-only access to that information (e.g. read-only access to Organization's admin/members and Repository's admin/content/metadata).

**Reasons**

Our org is moving to only allow fine-grained PATs and currently we can only get codeowners-validator to work with legacy PATs.
