Replace specific constant tests with just type checks #1731

Job	Run time
RuboCop	26s
specs (ubuntu, 3.0.6)	1m 30s
specs (ubuntu, 3.1.4)	1m 27s
specs (ubuntu, 3.2.2)	1m 26s
specs (ubuntu, 3.3.0)	1m 26s
specs (macos, 3.0.6)	1m 32s
specs (macos, 3.1.4)	1m 33s
specs (macos, 3.2.2)	1m 10s
specs (macos, 3.3.0)	1m 40s
specs (windows, 3.0.6)	4m 13s
specs (windows, 3.1.4)	4m 32s
specs (windows, 3.2.2)	5m 3s
specs (windows, 3.3.0)	3m 51s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 23s
	31m 12s

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