Bump actions/checkout from 5 to 6 (#181) #531

Job	Run time
ruby-versions / Generate Ruby versions	6s
windows-latest 2.7	1m 34s
windows-latest 3.3	59s
windows-latest 3.1	1m 8s
windows-latest jruby-head	1m 59s
windows-latest 3.0	1m 1s
windows-latest 3.4	1m 7s
windows-latest mingw	1m 0s
windows-latest 3.2	59s
windows-latest mswin	1m 28s
	11m 21s

Provide feedback