fix: specify rules variable type in org_policy_v2

[malhussan]

Without this change Terraform would throw an error because it's unable to infer types.

The issue is similar to https://github.com/hashicorp/terraform/issues/30592#issuecomment-1183689596, and its fix is by adding a type constraint.

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[prabhu34]

LGTM cc @prabhu34 for another pass

LGTM. Should rebase with main before the merge.

[comment-bot-dev]

@malhussan Thanks for the PR! 🚀
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