test

Bump required_ruby_version to 2.4.0 #49

Job	Run time
ruby-versions / Generate Ruby versions	3s
build (2.5 / ubuntu-latest)	27s
build (2.5 / macos-latest)	1m 6s
build (2.5 / windows-latest)	5m 28s
build (2.6 / ubuntu-latest)	22s
build (2.6 / macos-latest)	57s
build (2.6 / windows-latest)	4m 1s
build (2.7 / ubuntu-latest)	28s
build (2.7 / macos-latest)	54s
build (2.7 / windows-latest)	1m 41s
build (3.0 / ubuntu-latest)	9s
build (3.0 / macos-latest)	11s
build (3.0 / windows-latest)	2m 19s
build (3.1 / ubuntu-latest)	8s
build (3.1 / macos-latest)	13s
build (3.1 / windows-latest)	1m 4s
build (3.2 / ubuntu-latest)	8s
build (3.2 / macos-latest)	14s
build (3.2 / windows-latest)	3m 50s
build (head / ubuntu-latest)	10s
build (head / macos-latest)	17s
build (head / windows-latest)	2m 54s
build (jruby / ubuntu-latest)	25s
build (jruby / macos-latest)	52s
build (jruby / windows-latest)	2m 54s
build (jruby-head / ubuntu-latest)	27s
build (jruby-head / macos-latest)	41s
build (jruby-head / windows-latest)	4m 4s
build (truffleruby / ubuntu-latest)	18s
build (truffleruby / macos-latest)	2m 34s
build (truffleruby-head / ubuntu-latest)	29s
build (truffleruby-head / macos-latest)	36s
	40m 24s

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