Fix Content-Type allowlist bypass vulnerability remained #566

Job	Run time
RSpec and Cucumber (2.5, gemfiles/rails-6-0.gemfile, false)	1m 58s
RSpec and Cucumber (2.5, gemfiles/rails-6-0.gemfile, false)	1m 58s
RSpec and Cucumber (2.6, gemfiles/rails-6-0.gemfile, false)	2m 29s
RSpec and Cucumber (2.6, gemfiles/rails-6-0.gemfile, false)	2m 29s
RSpec and Cucumber (2.7, gemfiles/rails-6-0.gemfile, false)	2m 42s
RSpec and Cucumber (2.7, gemfiles/rails-6-0.gemfile, false)	2m 42s
RSpec and Cucumber (jruby, gemfiles/rails-6-0.gemfile, false)	3m 32s
RSpec and Cucumber (jruby, gemfiles/rails-6-0.gemfile, false)	3m 32s
RSpec and Cucumber (2.2, gemfiles/rails-5-0.gemfile, true)	2m 28s
RSpec and Cucumber (2.2, gemfiles/rails-5-0.gemfile, true)	2m 28s
RSpec and Cucumber (2.3, gemfiles/rails-5-1.gemfile, true)	9m 21s
RSpec and Cucumber (2.3, gemfiles/rails-5-1.gemfile, true)	2m 8s
RSpec and Cucumber (2.4, gemfiles/rails-5-2.gemfile, false)	2m 29s
RSpec and Cucumber (2.4, gemfiles/rails-5-2.gemfile, false)	2m 29s
RSpec and Cucumber (3, gemfiles/rails-6-1.gemfile, false)	1m 48s
RSpec and Cucumber (3, gemfiles/rails-6-1.gemfile, false)	1m 48s
RSpec and Cucumber (3, gemfiles/rails-master.gemfile, false)	1m 40s
RSpec and Cucumber (3, gemfiles/rails-master.gemfile, false)	1m 40s
RSpec and Cucumber (ruby-head, gemfiles/rails-6-1.gemfile, true)	2m 29s
RSpec and Cucumber (ruby-head, gemfiles/rails-6-1.gemfile, true)	2m 29s
RSpec and Cucumber (jruby-head, gemfiles/rails-6-0.gemfile, false)	2m 57s
RSpec and Cucumber (jruby-head, gemfiles/rails-6-0.gemfile, false)	2m 57s
	1h 0m 33s

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