Add conditional test dependency on `mutex_m` #18

Job	Run time
Test (Ruby 3.1, Rails 6.1.0)	14s
Test (Ruby 3.1, Rails 7.0.0)	12s
Test (Ruby 3.1, Rails 7.1.0)	13s
Test (Ruby 3.1, Rails edge)	50s
Test (Ruby 3.2, Rails 6.1.0)	14s
Test (Ruby 3.2, Rails 7.0.0)	16s
Test (Ruby 3.2, Rails 7.1.0)	9s
Test (Ruby 3.2, Rails edge)	22s
Test (Ruby 3.3, Rails 6.1.0)	12s
Test (Ruby 3.3, Rails 7.0.0)	11s
Test (Ruby 3.3, Rails 7.1.0)	10s
Test (Ruby 3.3, Rails edge)	17s
Test (Ruby jruby-head, Rails 6.1.0)	38s
Test (Ruby jruby-head, Rails 7.0.0)	45s
Test (Ruby jruby-head, Rails 7.1.0)	32s
Test (Ruby jruby-head, Rails edge)	1m 33s
Test (Ruby ruby-head, Rails 6.1.0)	15s
Test (Ruby ruby-head, Rails 7.0.0)	20s
Test (Ruby ruby-head, Rails 7.1.0)	17s
Test (Ruby ruby-head, Rails edge)	21s
Test (Ruby 2.6, Rails 6.1.0)	27s
Test (Ruby 2.7, Rails 6.1.0)	21s
Test (Ruby 2.7, Rails 7.0.0)	22s
Test (Ruby 3.0, Rails 6.1.0)	9s
Test (Ruby 3.0, Rails 7.0.0)	9s
Test (Ruby jruby-9.2, Rails 6.0.0)	52s
Test (Ruby jruby-9.2, Rails 6.1.0)	47s
Test (Ruby jruby-9.4, Rails 7.0.0)	36s
Test (Ruby 2.2, Rails 3.2.0)	28s
Test (Ruby 2.1, Rails 4.1.0)	14s
Test (Ruby 2.4, Rails 4.2.0)	24s
Test (Ruby 2.4, Rails 5.0.0)	20s
Test (Ruby 2.5, Rails 5.1.0)	23s
Test (Ruby 2.6, Rails 5.2.0)	31s
Test (Ruby 2.7, Rails 6.0.0)	31s
finish	8s
	14m 43s

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