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

```diff @@ 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](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/components?src=pr&el=components&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | Coverage Δ | | |---|---|---| | [sentry-ruby](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `98.51% <ø> (-0.14%)` | :arrow_down: | | [sentry-rails](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `97.19% <ø> (-0.76%)` | :arrow_down: | | [sentry-sidekiq](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `97.47% <ø> (+1.51%)` | :arrow_up: | | [sentry-resque](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `92.85% <ø> (+0.21%)` | :arrow_up: | | [sentry-delayed_job](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `95.65% <ø> (ø)` | | | [sentry-opentelemetry](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/components?src=pr&el=component&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry) | `99.31% <ø> (-0.69%)` | :arrow_down: | [see 17 files with indirect coverage changes](https://app.codecov.io/gh/getsentry/sentry-ruby/pull/2441/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=getsentry)