Revert "Enforce latest rubygems on CI (#2439)"

[solnic]

No idea what's going on but after merging in CI started failing. I cleared the bundle cache but it didn't help :( Reverting for now.

#skip-changelog

[codecov[bot]]

Codecov Report

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

Project coverage is 98.17%. Comparing base (957c8d6) to head (cee1a0a). Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2441      +/-   ##
==========================================
- Coverage   98.34%   98.17%   -0.17%     
==========================================
  Files         126      126              
  Lines        4705     4725      +20     
==========================================
+ Hits         4627     4639      +12     
- Misses         78       86       +8     

Components	Coverage Δ
sentry-ruby	98.51% <ø> (-0.14%)	:arrow_down:
sentry-rails	97.19% <ø> (-0.76%)	:arrow_down:
sentry-sidekiq	97.47% <ø> (+1.51%)	:arrow_up:
sentry-resque	92.85% <ø> (+0.21%)	:arrow_up:
sentry-delayed_job	95.65% <ø> (ø)
sentry-opentelemetry	99.31% <ø> (-0.69%)	:arrow_down:

see 17 files with indirect coverage changes