Drop required_ruby_version from gemspec #4

Job	Run time
build (gemfiles/Gemfile.activerecord-5.0, 2.4)	2m 25s
build (gemfiles/Gemfile.activerecord-6.1, 2.5)	1m 41s
build (gemfiles/Gemfile.activerecord-6.0, 2.5)	1m 40s
build (gemfiles/Gemfile.activerecord-8.0, 3.2)	2m 3s
build (gemfiles/Gemfile.activerecord-7.0, 2.7)	2m 7s
build (gemfiles/Gemfile.activerecord-5.2, 2.4)	2m 34s
build (gemfiles/Gemfile.activerecord-5.1, 2.4)	2m 25s
build (gemfiles/Gemfile.activerecord-7.1, 2.7)	2m 8s
build (gemfiles/Gemfile.activerecord-7.2, 3.1)	1m 44s
	18m 47s

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