Schema extensions are ignored on MacOS, but not on Linux

It looks like schema extensions are ignored on Mac, but not on Linux (x64). Is there a workaround?

## Steps to reproduce

* Clone https://github.com/rbalicki2/relay-test
* `yarn && yarn relay`

On Mac (platform: darwin, arch: arm64), this fails to compile, due to a missing field. On Linux (platform: linux, arch: x64), this successfully compiles.

The contents of the schema extension file can be arbitrary on Mac; it is never even parsed. However, it must exist.

Thank you!

Clone https://github.com/rbalicki2/relay-test and run `yarn && yarn relay` on macOS arm64 and Linux x64 to reproduce the platform difference. Start by tracing the Relay compiler entry point used by `yarn relay` and how it loads the schema extension file. Done means the extension is parsed and applied consistently on both platforms.

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