Prevent crashes from get_main_hub when in trap context

[solnic]

Fixes #2495

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 98.16%. Comparing base (14ef446) to head (eaf2b30).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
sentry-ruby/lib/sentry-ruby.rb	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2510      +/-   ##
==========================================
- Coverage   98.18%   98.16%   -0.02%     
==========================================
  Files         128      128              
  Lines        4846     4848       +2     
==========================================
+ Hits         4758     4759       +1     
- Misses         88       89       +1     

Components	Coverage Δ
sentry-ruby	98.54% <0.00%> (-0.03%)	⬇️
sentry-rails	97.07% <ø> (ø)
sentry-sidekiq	97.09% <ø> (ø)
sentry-resque	92.85% <ø> (+0.10%)	⬆️
sentry-delayed_job	95.65% <ø> (ø)
sentry-opentelemetry	99.31% <ø> (ø)

Files with missing lines	Coverage Δ
sentry-ruby/lib/sentry-ruby.rb	99.54% <0.00%> (-0.46%)	⬇️

... and 1 file with indirect coverage changes

[solnic]

@sl0thentr0py I set the spec to run only under 3.4+ because it was randomly failing on older ones and jruby has no fork. This is such an edge case and hub's going away so it makes no sense to pay the price for running a complex repro test on all rubies.