Description

Similar to getsentry/sentry-cocoa#2411

If the environment is not set for the SDK errors will default to production. However, sessions are sent without an environment.

Expected outcome: sessions would be sent with an environment
Actual outcome: sessions are sent without an environment set

Steps To Reproduce

1. set the environment and release options
2. Send an error event and session
3. Observe that session and error event with the correct environment
4. repeat without setting the environment option
5. Observe the error event with an environment of production
6. Observe the session with no environment