fix: Treat BusinessTeam as a regular Team for Environment reviewers

[JWilkinsonMB]

It is now supported to use Enterprise Teams as reviewers for Environments, however the type returned by the API has changed, so that instead of Team, it is now BusinessTeam. Sample JSON below:

{
  "reviewers": [
    {
      "type": "BusinessTeam",
      "reviewer": {
        "name": "Name",
        "id": 123456,
        "node_id": "ET_xyz123456",
        "slug": "ent:xyz123",
        "description": "",
        "privacy": "closed",
        "notification_setting": "notifications_enabled",
        "url": "https://api.github.com/enterprises/xyz/teams/123456",
        "html_url": "https://github.com/enterprises/xyz/teams/ent:desktop",
        "members_url": "https://api.github.com/enterprises/xyz/teams/123456/memberships{/member}",
        "repositories_url": "https://api.github.com/enterprises/xyz/teams/123456/repos",
        "type": "enterprise",
        "enterprise_id": 123,
        "permission": "pull",
        "parent": null
      }
    }
  ]
}

Prior to this PR this leads to an unmarshaling error if an enterprise team is included as a reviewer in any environment that the library tries to read.

Whilst there are some differences between a BusinessTeam and a Team such as enterprise_id instead of organization_id, a quick workaround is to treat both types as a Team given there is sufficient overlap which allows consumers such as the Terraform provider to be able to work without any breaking changes.

Fixes #4457

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.55%. Comparing base (27edd67) to head (b1c2291).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4456   +/-   ##
=======================================
  Coverage   97.55%   97.55%           
=======================================
  Files         194      194           
  Lines       19884    19890    +6     
=======================================
+ Hits        19398    19404    +6     
  Misses        268      268           
  Partials      218      218           

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[gmlewis]

@JWilkinsonMB - once you get the Google CLA signed, please let us know, and we can then proceed with this PR.

[JWilkinsonMB]

I'm still following up internally on the CLA, hopefully not too much longer