Fix flaky test for Debian package tracking events

Users::ActivityService can inject events during tests: https://gitlab.com/gitlab-org/gitlab/-/blob/97a9658c64da49fd6c14d1b6690762ff6ace4592/app/services/users/activity_service.rb#L46-56

Tighten down the conditions for matching a Snowplow event to prevent intermittent test failures.

Tentative fix for: #408126 (closed)