Skip sanity_check if APP_SECRET_TOKEN is defined

[knu]

Heroku is not the only running platform where environment variables are set outside of .env files, and APP_SECRET_TOKEN should be a good choice to determine if the environment is properly configured because bin/pre_runner_boot.rb already uses this variable to decide whether to call Dotenv.load.

[dsander]

That makes sense to me, thank you! I wonder why I have never run into this problem, I don't set the CI environment variable in my docker deployment.