[MAINT] Improve provider tests

[deiga]

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Before the change?

• It was possible to inadvertently set token and app_auth at the same time
• Some provider test's weren't actually testing anything

After the change?

• Ensures that token (or GITHUB_TOKEN) and app_auth can't be set at the same time
• Updated some provider tests to actually initialize the provider and verify changes

Pull request checklist

• Schema migrations have been created if needed (example)
• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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[github-actions]

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