[MAINT] Fix test of Org Repo Roles

[deiga]

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Before the change?

• Computed fields were not being set correctly in resource_github_organization_repository_role
• Tests for resource_github_organization_repository_role were failing due to configuration issues
• TODO comments for github_organization_repository_role about upgrading to v68+

After the change?

• Corrected behaviour of Computed fields
• Fixed tests
• Added validation for the permissions field in. resource_github_organization_repository_role
• Update to use new SDK functions

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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[stevehipwell]

LGTM

@deiga thanks for fixing these, I'm not sure how I managed to miss setting the repo_role. I'll get the API for listing the roles into the SDK, but with the current provider implementation I think we probably want to keep it static and use go generate to keep it up-to-date (my docs PR uses go generate so it should be straightforward to extend it for this an other potential uses.