Expand specs for Thread variables #1659

Job	Run time
specs (ubuntu, 3.0.6)	1m 27s
RuboCop	27s
specs (ubuntu, 3.1.4)	1m 31s
specs (ubuntu, 3.2.2)	1m 26s
specs (ubuntu, 3.3.0)	1m 22s
specs (macos, 3.0.6)	1m 20s
specs (macos, 3.1.4)	1m 21s
specs (macos, 3.2.2)	1m 13s
specs (macos, 3.3.0)	1m 8s
specs (windows, 3.0.6)	3m 35s
specs (windows, 3.1.4)	4m 0s
specs (windows, 3.2.2)	4m 9s
specs (windows, 3.3.0)	4m 54s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 25s
	29m 18s

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