Add specs for IO#autoclose? and IO#autoclose= (take 2) #1629

Job	Run time
RuboCop	25s
specs (ubuntu, 3.0.6)	1m 29s
specs (ubuntu, 3.1.4)	1m 26s
specs (ubuntu, 3.2.2)	1m 24s
specs (ubuntu, 3.3.0)	1m 26s
specs (macos, 3.0.6)	1m 59s
specs (macos, 3.1.4)	2m 11s
specs (macos, 3.2.2)	1m 56s
specs (macos, 3.3.0)	1m 11s
specs (windows, 3.0.6)	3m 43s
specs (windows, 3.1.4)	5m 2s
specs (windows, 3.2.2)	5m 1s
specs (windows, 3.3.0)	5m 15s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 25s
	33m 53s

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