Add spec for compare_by_identity behaviour of Hash#replace #1635

Job	Run time
specs (ubuntu, 3.0.6)	1m 27s
RuboCop	28s
specs (ubuntu, 3.1.4)	1m 31s
specs (ubuntu, 3.2.2)	1m 26s
specs (ubuntu, 3.3.0)	1m 24s
specs (macos, 3.0.6)	1m 45s
specs (macos, 3.1.4)	1m 46s
specs (macos, 3.2.2)	1m 9s
specs (macos, 3.3.0)	1m 8s
specs (windows, 3.0.6)	4m 5s
specs (windows, 3.1.4)	4m 41s
specs (windows, 3.2.2)	6m 44s
specs (windows, 3.3.0)	4m 14s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 35s
	33m 23s

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