Add sentry integration tests

[maudetes]

Following #2620, add integration tests for sentry, in particular to test flask and celery events catching.

Possible Implementation

You can look at the following doc for testing: https://docs.sentry.io/platforms/python/guides/flask/configuration/options/#transport, https://flask.palletsprojects.com/en/2.0.x/testing/ and https://docs.celeryproject.org/en/stable/userguide/testing.html?highlight=testing.