Ruby

Support RBS::AST::Members::InstanceVariable #1131

Job	Run time
ruby-versions / Generate Ruby versions	4s
build (3.2)	43s
build (truffleruby)	35s
build (3.4)	41s
build (head)	42s
build (truffleruby-head)	32s
build (3.3)	42s
	3m 59s

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