Scrub header values with invalid encoding

[st0012]

Closes #1551

[codecov-commenter]

Codecov Report

Merging #1552 (16a0713) into master (740ed8c) will increase coverage by 0.36%.
The diff coverage is 100.00%.

❗ Current head 16a0713 differs from pull request most recent head ca6d2fd. Consider uploading reports for the commit ca6d2fd to get more accurate results

@@            Coverage Diff             @@
##           master    #1552      +/-   ##
==========================================
+ Coverage   97.91%   98.27%   +0.36%     
==========================================
  Files         222      127      -95     
  Lines       10855     7030    -3825     
==========================================
- Hits        10629     6909    -3720     
+ Misses        226      121     -105     

Impacted Files	Coverage Δ
sentry-ruby/lib/sentry/interfaces/request.rb	95.31% <100.00%> (+0.48%)	⬆️
...y/spec/sentry/interfaces/request_interface_spec.rb	99.18% <100.00%> (+0.04%)	⬆️
sentry-rails/app/jobs/sentry/send_event_job.rb	81.25% <0.00%> (-6.25%)	⬇️
sentry-raven/spec/raven/configuration_spec.rb
...-raven/spec/raven/integrations/rails/event_spec.rb
sentry-raven/lib/raven/processor/sanitizedata.rb
sentry-raven/lib/raven/configuration.rb
sentry-raven/spec/raven/integration_spec.rb
...try-raven/lib/raven/utils/exception_cause_chain.rb
sentry-raven/lib/raven/processor/utf8conversion.rb
... and 88 more

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