feat: Allow OrganizationRole bypass actor type in rulesets

[marcencov]

Resolves #3674

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Before the change?

• github_repository_ruleset and github_organization_ruleset rejected actor_type = "OrganizationRole" in bypass_actors, failing with expected actor_type to be one of [...].
• Rulesets with custom organization roles in the bypass list (for example ones configured in the UI) could not be managed: Terraform planned to remove the bypass actor and could not add it back.

After the change?

• OrganizationRole is accepted as a bypass actor type in both resources. actor_id is the organization role ID (for example github_organization_role.x.role_id).
• The docs list OrganizationRole as a valid value.
• Acceptance tests added for both resources: each creates a custom organization role and uses it as a bypass actor. They require an Enterprise organization and have not been run against GitHub yet; unit tests pass.

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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