Add spec for regexp compilation with invalid characters #285

Job	Run time
RuboCop	28s
specs (ubuntu, 3.0.6)	1m 32s
specs (ubuntu, 3.1.4)	1m 27s
specs (ubuntu, 3.2.2)	1m 28s
specs (ubuntu, 3.3.0)	1m 24s
specs (macos, 3.0.6)	1m 36s
specs (macos, 3.1.4)	1m 19s
specs (macos, 3.2.2)	1m 9s
specs (macos, 3.3.0)	1m 9s
specs (windows, 3.0.6)	4m 41s
specs (windows, 3.1.4)	4m 54s
specs (windows, 3.2.2)	4m 2s
specs (windows, 3.3.0)	4m 13s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 23s
	30m 45s

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