I recently added new ENV variables to my app, this is particularly my STRIPE_SECRET_KEY in an initializer:
Stripe.api_key = ENV.fetch("STRIPE_SECRET_KEY")
When I push my code up to my staging server and the tests run this error pops up. I made certain the variable is set on my staging server, I updated my app.json file as well to require these variables, I tried stopping Spring as well, nothing makes the error go away.
It's not recommended to include sensitive config variables in your app.json. If you have anything like that checked in, I'd recommend dropping it. Instead, you can add those to the CI environment through the web GUI. The instructions for how to do that are here. When you've added the correct key there you should be able to run CI without this error.