Add spec for regexp compilation with invalid characters #1753

Job	Run time
RuboCop	26s
specs (ubuntu, 3.0.6)	1m 41s
specs (ubuntu, 3.1.4)	1m 37s
specs (ubuntu, 3.2.2)	1m 29s
specs (ubuntu, 3.3.0)	1m 27s
specs (macos, 3.0.6)	1m 21s
specs (macos, 3.1.4)	1m 19s
specs (macos, 3.2.2)	1m 10s
specs (macos, 3.3.0)	1m 7s
specs (windows, 3.0.6)	3m 47s
specs (windows, 3.1.4)	5m 14s
specs (windows, 3.2.2)	4m 45s
specs (windows, 3.3.0)	4m 42s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 25s
	31m 30s

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