Add `expect_syntax_error` spec helper #1728

Job	Run time
RuboCop	27s
specs (ubuntu, 3.0.6)	1m 36s
specs (ubuntu, 3.1.4)	1m 27s
specs (ubuntu, 3.2.2)	1m 29s
specs (ubuntu, 3.3.0)	1m 24s
specs (macos, 3.0.6)	1m 23s
specs (macos, 3.1.4)	1m 35s
specs (macos, 3.2.2)	1m 9s
specs (macos, 3.3.0)	1m 14s
specs (windows, 3.0.6)	4m 11s
specs (windows, 3.1.4)	4m 36s
specs (windows, 3.2.2)	4m 59s
specs (windows, 3.3.0)	5m 54s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 27s
	32m 51s

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