Bump express from 4.18.2 to 4.21.0 in /sentry-rails/examples/rails-6.0 #8

Job	Run time
Ruby 2.7 & Sidekiq 5.0, options - null	1m 9s
Ruby 3.0 & Sidekiq 5.0, options - null	1m 4s
Ruby 3.1 & Sidekiq 5.0, options - null	1m 17s
Ruby 3.2 & Sidekiq 5.0, options - null	1m 13s
Ruby 3.3 & Sidekiq 5.0, options - null	1m 3s
Ruby jruby & Sidekiq 5.0, options - null	1m 47s
Ruby 2.7 & Sidekiq 6.5, options - null	1m 6s
Ruby 3.0 & Sidekiq 6.5, options - null	59s
Ruby 3.1 & Sidekiq 6.5, options - null	1m 6s
Ruby 3.2 & Sidekiq 6.5, options - null	1m 7s
Ruby 3.3 & Sidekiq 6.5, options - null	1m 11s
Ruby jruby & Sidekiq 6.5, options - null	1m 33s
Ruby 2.7 & Sidekiq 7.0, options - null	1m 19s
Ruby 3.0 & Sidekiq 7.0, options - null	54s
Ruby 3.1 & Sidekiq 7.0, options - null	44s
Ruby 3.2 & Sidekiq 7.0, options - { "codecov": 1 }	52s
Ruby 3.3 & Sidekiq 7.0, options - null	50s
Ruby jruby & Sidekiq 7.0, options - null	1m 30s
Ruby 2.4 & Sidekiq 5, options - null	1m 25s
Ruby 2.5 & Sidekiq 5, options - null	53s
Ruby 2.5 & Sidekiq 6, options - null	51s
Ruby 2.6 & Sidekiq 5, options - null	1m 8s
Ruby 2.6 & Sidekiq 6, options - null	59s
Ruby jruby & Sidekiq 6, options - null	1m 24s
	27m 24s

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