Update `CONTRIBUTING.md` to include `Simplecov` #2506

Job	Run time
Test coverage	22s
Edge RuboCop: internal_investigation	11s
Edge RuboCop: spec	18s
Ruby 2.7: internal_investigation	26s
Confirm config and documentation	9s
Ruby 2.7: spec	30s
Ruby 3.0: internal_investigation	10s
Ruby 3.0: spec	16s
Oldest RuboCop: spec	19s
Ruby 3.1: internal_investigation	11s
Ruby 3.1: spec	17s
Ruby 3.2: internal_investigation	12s
Ruby 3.2: spec	17s
Ruby 3.3: internal_investigation	10s
Ruby 3.3: spec	16s
Ruby 3.4: internal_investigation	10s
Ruby 3.4: spec	17s
Ruby ruby-head: internal_investigation	11s
Ruby ruby-head: spec	24s
Ruby jruby-9.4: internal_investigation	1m 19s
Ruby jruby-9.4: spec	1m 19s
Prism	30s
RSpec 4	17s
	8m 31s

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