Fix regression with CheckInEvent in before_send

[sl0thentr0py]

closes #2540

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.39%. Comparing base (b5a4948) to head (d068d34).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2541      +/-   ##
==========================================
- Coverage   69.40%   69.39%   -0.01%     
==========================================
  Files         126      126              
  Lines        4723     4725       +2     
==========================================
+ Hits         3278     3279       +1     
- Misses       1445     1446       +1     

Components	Coverage Δ
sentry-ruby	60.19% <ø> (ø)
sentry-rails	97.48% <ø> (ø)
sentry-sidekiq	95.52% <ø> (-0.38%)	⬇️
sentry-resque	92.64% <ø> (ø)
sentry-delayed_job	95.65% <ø> (ø)
sentry-opentelemetry	100.00% <ø> (ø)

Files with missing lines	Coverage Δ
sentry-ruby/lib/sentry/client.rb	48.52% <ø> (ø)

... and 1 file with indirect coverage changes