update fastlane to use Scanfile (#29963)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29963
### Summary
To run unit tests via Fastlane, simply run `fastlane scan`. Under the hood, it uses `xcodebuild` to run the unit tests. The Scanfile serves as a config file for Fastlane where you can specify parameters you want to pass to `xcodebuild`. More about Scan - https://docs.fastlane.tools/actions/scan/
### Test Plan
- `fastlane scan` is able to run on CI machines.
Test Plan: Imported from OSS
Differential Revision: D18606098
Pulled By: xta0
fbshipit-source-id: b4727d964fa56076b2ff383b40d1b13607721394
