Match error messages in specs of Array#fetch #2271

Job	Run time
RuboCop	47s
specs (ubuntu, 3.2.9)	1m 32s
specs (macos, 3.2.9)	1m 38s
specs (ubuntu, 4.0.0)	1m 30s
specs (ubuntu, 3.4.8)	1m 36s
specs (windows, 4.0.0)	3m 32s
specs (windows, 3.4.8)	3m 22s
specs (windows, 3.3.10)	3m 13s
specs (ubuntu, 3.3.10)	1m 33s
specs (windows, 3.2.8)	3m 40s
specs (ubuntu, 4.0.0, --repeat 2)	2m 18s
specs (macos, 3.3.10)	1m 47s
specs (macos, 3.4.8)	1m 47s
specs (ubuntu, 4.0.0, --enable-frozen-string-literal)	1m 31s
specs (ubuntu, 4.0.0, --parser=parse.y)	1m 35s
specs (macos, 4.0.0)	1m 36s
	32m 57s

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