Add `not_publish_event` rspec matcher

What does this MR do and why?

Creates a not_publish_event matcher, for the Gitlab Event Store, to avoid multiple examples just to add more assertions for a test. I firstly faced that in in !98125 (merged), and decided extract the matcher in this single MR.

Example

    it 'does not create a pages domain and does not publish a PagesDomainCreatedEvent' do
      expect { service.execute }
        .to not_publish_event(PagesDomains::PagesDomainCreatedEvent)
        .and not_change(project.pages_domains, :count)
    end

Related to:

• https://docs.gitlab.com/ee/development/testing_guide/best_practices.html#avoid-repeating-expensive-actions

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