[BE][GHF] Do not call GraphQL twice (#100434)
During regular merge process, `GitHubPR` and `GitHubRepo` objects are first created in main() and than re-created in `merge()` instead of being passed by reference, which results in making the same GraphQL requests to the repo twice
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### <samp>🤖 Generated by Copilot at ee4e23e</samp>
> _Sing, O Muse, of the skillful coder who refactored_
> _The `merge` function, to accept a `GitHubPR` object,_
> _And thus reduced the calls to the divine API_
> _And the duplication of code, that source of errors._
Pull Request resolved: https://github.com/pytorch/pytorch/pull/100434
Approved by: https://github.com/kit1980, https://github.com/PaliC, https://github.com/huydhn, https://github.com/ZainRizvi
