Fix an error for `RSpecRails/HttpStatus` when no rack gem is loaded with rubocop-rspec #25

Job	Run time
Test coverage	10s
Edge RuboCop: internal_investigation	11s
Confirm config and documentation	12s
Edge RuboCop: spec	12s
Edge RuboCop RSpec: internal_investigation	32s
Edge RuboCop RSpec: spec	11s
Ruby 2.7: internal_investigation	22s
RSpec 4	12s
Ruby 2.7: spec	23s
Ruby 3.0: internal_investigation	12s
Ruby 3.0: spec	14s
Ruby 3.1: internal_investigation	10s
Ruby 3.1: spec	14s
Ruby 3.2: internal_investigation	12s
Ruby 3.2: spec	17s
Ruby 3.3: internal_investigation	10s
Ruby 3.3: spec	11s
Ruby ruby-head: internal_investigation	20s
Ruby ruby-head: spec	16s
Ruby jruby-9.4: internal_investigation	46s
Ruby jruby-9.4: spec	48s
	6m 15s

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