sidekiq-throttled.gemspec: Prefer add_dependency

[olleolleolle]

This is a lint change, in order to get builds to 🟢

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.97%. Comparing base (39f3f78) to head (ffbf68a). Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #192   +/-   ##
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  Coverage   98.97%   98.97%           
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  Files          19       19           
  Lines         390      390           
  Branches       56       56           
=======================================
  Hits          386      386           
  Misses          4        4           

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[ixti]

Thank you! And sorry, missed this PR - closed via f1a86f12bf9660e5515620175f2633510fe4d4e7