Add 3.1.9 release note #594

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 2.7	42s
ubuntu-24.04 3.2	13s
ubuntu-24.04 3.3	18s
ubuntu-24.04 3.1	17s
ubuntu-24.04 3.0	15s
ubuntu-24.04 head	14s
ubuntu-22.04 3.0	18s
ubuntu-22.04 2.7	46s
ubuntu-22.04 jruby-head	1m 7s
ubuntu-24.04 3.4	16s
ubuntu-22.04 3.2	17s
ubuntu-22.04 truffleruby-head	27s
ubuntu-24.04 jruby-head	1m 10s
ubuntu-22.04 3.1	18s
ubuntu-22.04 3.3	15s
ubuntu-22.04 head	13s
ubuntu-24.04 truffleruby-head	25s
ubuntu-22.04 debug	21s
ubuntu-22.04 3.4	14s
ubuntu-24.04 debug	20s
	8m 30s

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