Merge pull request #82 from k0kubun/release-3-1-1 #180

Job	Run time
ruby-versions / Generate Ruby versions	3s
build (2.5 / ubuntu-latest)	21s
build (2.5 / windows-latest)	2m 32s
build (2.6 / ubuntu-latest)	24s
build (2.6 / macos-latest)	29s
build (2.6 / windows-latest)	3m 33s
build (2.7 / ubuntu-latest)	25s
build (2.7 / macos-latest)	58s
build (2.7 / windows-latest)	2m 53s
build (3.0 / ubuntu-latest)	15s
build (3.0 / macos-latest)	16s
build (3.0 / windows-latest)	2m 1s
build (3.1 / ubuntu-latest)	18s
build (3.1 / macos-latest)	16s
build (3.1 / windows-latest)	2m 27s
build (3.2 / ubuntu-latest)	17s
build (3.2 / macos-latest)	20s
build (3.2 / windows-latest)	3m 33s
build (3.3 / ubuntu-latest)	17s
build (3.3 / macos-latest)	16s
build (3.3 / windows-latest)	3m 12s
build (head / ubuntu-latest)	10s
build (head / macos-latest)	17s
build (truffleruby-head / ubuntu-latest)	33s
build (truffleruby-head / macos-latest)	32s
build (mswin / windows-latest)	2m 58s
build (mingw / windows-latest)	3m 14s
	32m 50s

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