Add 3.1.9 release note #535

Job	Run time
ruby-versions / Generate Ruby versions	3s
windows-latest 3.0	1m 4s
windows-latest 3.1	1m 11s
windows-latest jruby-head	1m 42s
windows-latest 2.7	1m 45s
windows-latest 3.4	1m 24s
windows-latest mswin	1m 18s
windows-latest 3.2	1m 1s
windows-latest 3.3	1m 2s
windows-latest mingw	56s
	11m 26s

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