Add 3.1.2 entry #331

Job	Run time
ruby-versions / Generate Ruby versions	2s
windows-latest 2.7	2m 56s
windows-latest 3.0	1m 24s
windows-latest 3.1	1m 29s
windows-latest 3.2	2m 26s
windows-latest 3.3	3m 0s
windows-latest mingw	1m 9s
windows-latest mswin	1m 46s
	14m 12s

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