[rails] support string errors in error reporter

[solnic]

Closes #2460

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.13%. Comparing base (5de4ebc) to head (5f92f21).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2464   +/-   ##
=======================================
  Coverage   98.13%   98.13%           
=======================================
  Files         126      126           
  Lines        4761     4767    +6     
=======================================
+ Hits         4672     4678    +6     
  Misses         89       89           

Components	Coverage Δ
sentry-ruby	98.51% <ø> (ø)
sentry-rails	97.08% <100.00%> (+0.02%)	⬆️
sentry-sidekiq	96.96% <ø> (ø)
sentry-resque	92.85% <ø> (ø)
sentry-delayed_job	95.65% <ø> (ø)
sentry-opentelemetry	99.31% <ø> (ø)

Files with missing lines	Coverage Δ
sentry-rails/lib/sentry/rails/error_subscriber.rb	100.00% <100.00%> (ø)