Upgrade to Sidekiq 8 and Rack 3

[rgalanakis]

See lithictech/appydays#18 and lithictech/sidekiq-amigo#19

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.34%. Comparing base (f7c4486) to head (85b2e51).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #825      +/-   ##
==========================================
+ Coverage   99.31%   99.34%   +0.03%     
==========================================
  Files         576      577       +1     
  Lines       27622    27682      +60     
==========================================
+ Hits        27432    27502      +70     
+ Misses        190      180      -10     

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