Fix flaky spec in record fetcher

Ref: #383028 (closed)

What does this MR do and why?

This MR fixes a flaky spec identified while removing Timecop references in !101499 (merged).

It turns out let_it_be is called before the around block where the time was frozen.

To fix this spec, we are now freezing the time with before_all which is called right before let_it_be.

bundle exec rspec --order defined ./spec/lib/gitlab/analytics/cycle_analytics/records_fetcher_spec.rb

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