ci: freeze time in more specs

[santib]

Example of failure https://github.com/santib/rack-attack/actions/runs/7199119786/job/19610109965

# Running:

........F

Failure:
ActiveSupport::Cache::MemoryStore as a cache backend#test_0002_works for fail2ban [/home/runner/work/rack-attack/rack-attack/spec/support/cache_store_helper.rb:36]:
Expected: 403
  Actual: 200

bin/rails test /home/runner/work/rack-attack/rack-attack/spec/support/cache_store_helper.rb:19

..........................................................................S....................................................................

Finished in 2.172762s, 69.9571 runs/s, 132.5502 assertions/s.
[15](https://github.com/santib/rack-attack/actions/runs/7199119786/job/19610109965#step:5:16)2 runs, 288 assertions, 1 failures, 0 errors, 1 skips