Tests

Fix: explicitly require racc and ostruct. #1149

Job	Run time
test (ruby=2.7)	31s
test (ruby=2.7, concurrency=async-websocket)	32s
test (ruby=3.0)	26s
test (ruby=3.1)	32s
test (ruby=3.2)	31s
test (ruby=3.3)	22s
test (ruby=ruby-head)	21s
test (ruby=jruby-head)	1m 44s
coveralls	0s
	4m 59s

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