Add conditional test dependency on `base64`, `mutex_m`, `bigdecimal` #21

Job	Run time
Test (Ruby 3.1, Rails 6.1.0)	15s
Test (Ruby 3.1, Rails 7.0.0)	15s
Test (Ruby 3.1, Rails 7.1.0)	15s
Test (Ruby 3.1, Rails edge)	37s
Test (Ruby 3.2, Rails 6.1.0)	11s
Test (Ruby 3.2, Rails 7.0.0)	12s
Test (Ruby 3.2, Rails 7.1.0)	10s
Test (Ruby 3.2, Rails edge)	11s
Test (Ruby 3.3, Rails 6.1.0)	12s
Test (Ruby 3.3, Rails 7.0.0)	13s
Test (Ruby 3.3, Rails 7.1.0)	10s
Test (Ruby 3.3, Rails edge)	12s
Test (Ruby jruby-head, Rails 6.1.0)	35s
Test (Ruby jruby-head, Rails 7.0.0)	44s
Test (Ruby jruby-head, Rails 7.1.0)	36s
Test (Ruby jruby-head, Rails edge)	53s
Test (Ruby ruby-head, Rails 6.1.0)	18s
Test (Ruby ruby-head, Rails 7.0.0)	22s
Test (Ruby ruby-head, Rails 7.1.0)	23s
Test (Ruby ruby-head, Rails edge)	23s
Test (Ruby 2.6, Rails 6.1.0)	24s
Test (Ruby 2.7, Rails 6.1.0)	21s
Test (Ruby 2.7, Rails 7.0.0)	25s
Test (Ruby 3.0, Rails 6.1.0)	10s
Test (Ruby 3.0, Rails 7.0.0)	14s
Test (Ruby jruby-9.2, Rails 6.0.0)	57s
Test (Ruby jruby-9.2, Rails 6.1.0)	53s
Test (Ruby jruby-9.4, Rails 7.0.0)	40s
Test (Ruby 2.2, Rails 3.2.0)	27s
Test (Ruby 2.1, Rails 4.1.0)	16s
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)	24s
Test (Ruby 2.6, Rails 5.2.0)	27s
Test (Ruby 2.7, Rails 6.0.0)	27s
finish	3s
	13m 59s

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