Use `by lazy(LazyThreadSafetyMode.NONE)` for RNTester (#52886)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52886

RNTester was using just a plain `by lazy{}` which gets flagged by our internal linter over and over.
This fixes it.

Changelog:
[Internal] [Changed] -

Reviewed By: mdvacca

Differential Revision: D79094496

fbshipit-source-id: 856864bf8b5e4ec1254d1793dba9e97377696408