Possibly incorrect type for visibility field in repository schemas

[mariusknaust]

The visibility field from the nebula preview in /components/schemas/{repository, team-repository, full-repository} is listed as a plain string unlike the other occurrences of the visibility field where it is listed as a string enum. This is probably an error, as the description states the enum values.

visibility:
          description: 'The repository visibility: public, private, or internal.'
          type: string
          example: public