Add 3.1.9 release note #595

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-24.04 3.1	17s
ubuntu-24.04 3.2	17s
ubuntu-24.04 3.4	17s
ubuntu-24.04 2.7	42s
ubuntu-24.04 3.0	16s
ubuntu-24.04 jruby-head	1m 3s
ubuntu-24.04 head	13s
ubuntu-24.04 debug	21s
ubuntu-24.04 3.3	16s
ubuntu-22.04 2.7	40s
ubuntu-24.04 truffleruby-head	29s
ubuntu-22.04 3.2	15s
ubuntu-22.04 3.1	16s
ubuntu-22.04 3.4	16s
ubuntu-22.04 debug	30s
ubuntu-22.04 3.0	13s
ubuntu-22.04 3.3	24s
ubuntu-22.04 truffleruby-head	28s
ubuntu-22.04 head	12s
ubuntu-22.04 jruby-head	1m 9s
	8m 38s

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