Summary:
[Fixes an issue where the Docker Android tests container cannot be built.](https://github.com/facebook/react-native/pull/24276#issuecomment-480915232) The JSC is now pulled from the npm registry, so we need to run `yarn` prior to pulling the Gradle dependencies.

[Android] [Fixed] - Fixed React Native Android tests Docker container issue related to the JSC
Pull Request resolved: https://github.com/facebook/react-native/pull/24360

Differential Revision: D14842534

Pulled By: hramos

fbshipit-source-id: 3a1a714879e9c52a812b1077dce449470c30bddd