doc: Fix usage example for github_app_installation_repositories

[ViacheslavKudinov]

Resolves #3119

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Before the change?

• usage snippet had extra ending double quote and page title also was wrong

After the change?

• removed quote, updated page title, formatted snippet if it was done by terraform fmt

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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