[docs] update repository_environment resource documentation

[LarsFronius]

This is relatively analogous to #3266 in which the data source was updated with a note regarding verifying permissions as they were non-obvious.
This adds a similar comment to the repository_environment resource and references the PUT instead of the GET endpoint.

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Before the change?

• It wasn't obvious which permissions a github_repository_environment required.

After the change?

• It's more obvious.

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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