use instance_for_test in test_event_callback function
Summary: I was looking at this test investigating flakiness and I notice it was using the forbidden method for testing (DagsterInstance.local_temp()) I doubt this will fix the issue described in #3169 but a good excuse to replace this callsite.
Test Plan: BK
Reviewers: max, dgibson
Reviewed By: dgibson
Differential Revision: https://dagster.phacility.com/D4972