Split multibyte class names from Marshal fixtures into their own file #1750

Job	Run time
RuboCop	25s
specs (ubuntu, 3.0.6)	1m 35s
specs (ubuntu, 3.1.4)	1m 37s
specs (ubuntu, 3.2.2)	1m 37s
specs (ubuntu, 3.3.0)	1m 30s
specs (macos, 3.0.6)	1m 49s
specs (macos, 3.1.4)	1m 43s
specs (macos, 3.2.2)	1m 16s
specs (macos, 3.3.0)	1m 9s
specs (windows, 3.0.6)	3m 54s
specs (windows, 3.1.4)	5m 24s
specs (windows, 3.2.2)	5m 23s
specs (windows, 3.3.0)	4m 23s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 27s
	33m 12s

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