Fix flaky ingest reports service spec

What does this MR do and why?

Some of the tests in ee/spec/services/security/ingestion/ingest_reports_service_spec.rb file are flaky.

This can be reproduced by running the specs in this file with seed 27931;

bundle exec rspec ee/spec/services/security/ingestion/ingest_reports_service_spec.rb --seed 27931