Bump actions/checkout from 4 to 5 #422

Job	Run time
ruby-versions / Generate Ruby versions	4s
windows-latest 3.2	47s
windows-latest 2.7	1m 14s
windows-latest 3.1	47s
windows-latest 3.0	46s
windows-latest 3.3	42s
windows-latest 3.4	53s
windows-latest jruby-head	1m 26s
windows-latest mingw	1m 9s
windows-latest mswin	59s
	8m 47s

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