[MAINT] Consolidate ID format of github_emu_group_mapping

[deiga]

Resolves #3200

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Before the change?

• Import ID and Resource ID had different format
• tflog.SetField was being used incorrectly
• Tests didn't use terraform-plugin-testing
• Some tests didn't fully work
• Docs were missing computed fields

After the change?

• Import ID and Resource ID have the same format
• Fixes tflog.SetField usage
• Updates tests to use terraform-plugin-testing
• Fixed tests
• Updates docs

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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