Disable Express' automatic registration/version checking in a testing environment

[brandonsturgeon]

When running our GLuaTest suite in Github's Actions, Express still reaches out to the default domain and does a revision check and registration.

This is unnecessary for our use case, so we should tell Express not to bother when it's in such an environment.

There may be a convar we can check (or create) that would indicate it's in a test environment. A little bit of discovery is necessary for this.