[Django]-Why are assertions being logged in sentry when DEBUG = True?

In raven-python 3.0.0 DEBUG setting in Django no longer disables Raven.
From documentation:

Raven to install a hook in Django that will automatically report
uncaught exceptions

In your case, assert generate uncaught exceptions AssertionError, which logged in Sentry.

To disable this functionality set dsn = None or remove dsn (source):

 RAVEN_CONFIG = {
    'dsn': None
 }