Add a comment to explicit RUBY_FL_USER2 | RUBY_FL_USER3 (#133) #463

Job	Run time
ruby-versions / Generate Ruby versions	3s
ubuntu-24.04 2.7	47s
ubuntu-24.04 3.0	16s
ubuntu-24.04 3.1	11s
ubuntu-24.04 3.2	16s
ubuntu-24.04 3.3	26s
ubuntu-24.04 3.4	14s
ubuntu-24.04 debug	27s
ubuntu-24.04 head	18s
ubuntu-24.04 jruby-head	1m 3s
ubuntu-24.04 truffleruby-head	29s
ubuntu-22.04 2.7	48s
ubuntu-22.04 3.0	22s
ubuntu-22.04 3.1	15s
ubuntu-22.04 3.2	15s
ubuntu-22.04 3.3	16s
ubuntu-22.04 3.4	15s
ubuntu-22.04 debug	17s
ubuntu-22.04 head	21s
ubuntu-22.04 jruby-head	1m 4s
ubuntu-22.04 truffleruby-head	32s
	8m 55s

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