[Feature Request] Add warnings when globals aren't injected

[Matan Borenkraout]

Describe the feature you'd like:

As a followup to #1240.
If a user isn't injecting globals (like in vitest), they need to call cleanup on their own and also set the REACT_IS_ACT_ENVIRONMENT. In case they aren't doing that, we should warn them because this will break the behavior.

Suggested implementation:

We can log a warning in case globals aren't injected, but this won't cover the option where users can call cleanup on their own.