Fix RSpec/TimecopFreeze offenses (Part 1/2)

What does this MR do and why?

🚫 This MR depends on !76030 (merged).

This fixes some of the remaining RSpec/TimecopFreeze offenses in:

• ee/spec/lib/gitlab/analytics/cycle_analytics/data_collector_spec.rb
• ee/spec/lib/gitlab/insights/reducers/count_per_period_reducer_spec.rb

This MR is part 1 of a 2 part series of MRs to resolve RSpec/TimecopFreeze of #214432 (closed).

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.