Add specs for Data#to_h #1746

Job	Run time
RuboCop	26s
specs (ubuntu, 3.0.6)	1m 27s
specs (ubuntu, 3.1.4)	1m 29s
specs (ubuntu, 3.2.2)	1m 30s
specs (ubuntu, 3.3.0)	1m 22s
specs (macos, 3.0.6)	1m 35s
specs (macos, 3.1.4)	1m 16s
specs (macos, 3.2.2)	1m 7s
specs (macos, 3.3.0)	1m 8s
specs (windows, 3.0.6)	5m 9s
specs (windows, 3.1.4)	4m 58s
specs (windows, 3.2.2)	4m 40s
specs (windows, 3.3.0)	4m 43s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 24s
	32m 14s

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