Run build for the test project in github actions (#3696)
Run build for the test project in github actions (#3696)

Summary:
This is a "smoke" test, to make sure we can build an example project on all platforms without errors.

I think later, we can also add snapshot testing/flow test on this project to make sure we don't have unexpected changes in the output.

Pull Request resolved: https://github.com/facebook/relay/pull/3696

Test Plan:
The output of the new step:
```
     Running `target\debug\relay.exe ./test-project/relay.json`
[test] compiling...
[test] compiled documents: 2 reader, 1 normalization, 2 operation text
Done
```

**Static Docs Preview: relay**
|[Full Site](https://our.intern.facebook.com/intern/staticdocs/eph/D33169332/V2/relay/)|

|**Modified Pages**|

Reviewed By: tyao1

Differential Revision: D33169332

Pulled By: alunyov

fbshipit-source-id: a174fc97510628ea31c1c6443a169f699b23651e

kassens/relay,josephsavona/relay,facebook/relay,kassens/relay,josephsavona/relay,kassens/relay,voideanvalue/relay,xuorig/relay,facebook/relay,xuorig/relay,josephsavona/relay,wincent/relay,wincent/relay,wincent/relay,wincent/relay,xuorig/relay,facebook/relay,xuorig/relay,voideanvalue/relay,wincent/relay,xuorig/relay,voideanvalue/relay,kassens/relay,voideanvalue/relay,facebook/relay,facebook/relay,facebook/relay,voideanvalue/relay,wincent/relay,kassens/relay,kassens/relay,xuorig/relay,voideanvalue/relay