Add a comment to explicit RUBY_FL_USER2 | RUBY_FL_USER3 #461

Job	Run time
ruby-versions / Generate Ruby versions	2s
ubuntu-24.04 2.7	42s
ubuntu-24.04 3.0	16s
ubuntu-24.04 3.1	14s
ubuntu-24.04 3.2	17s
ubuntu-24.04 3.3	10s
ubuntu-24.04 3.4	15s
ubuntu-24.04 debug	18s
ubuntu-24.04 head	17s
ubuntu-24.04 jruby-head	1m 4s
ubuntu-24.04 truffleruby-head	31s
ubuntu-22.04 2.7	41s
ubuntu-22.04 3.0	14s
ubuntu-22.04 3.1	15s
ubuntu-22.04 3.2	20s
ubuntu-22.04 3.3	16s
ubuntu-22.04 3.4	11s
ubuntu-22.04 debug	20s
ubuntu-22.04 head	16s
ubuntu-22.04 jruby-head	1m 1s
ubuntu-22.04 truffleruby-head	26s
	8m 6s

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