When a process terminates, both the extension managers and integration

managers are shut down, clearing all state. The order in which this

happens is not guaranteed, and it's very possible (and likely) for the

integration managers to shut down before the extension managers. When

this happens, any integrations registered by an extension through

BaseIntegrationHook will fail to unregister, leaving a handful of errors

in the console or logs.
We now have an enabled state on IntegrationManager that indicates

whether operations can be performed on the manager. This is set when

initialized, and cleared after calling shutdown(). BaseIntegrationHook

now checks this before attempting to unregister, keeping logs clean.

Ran some management commands and stopped seeing errors during shutdown.
Unit tests pass.