Use proper type for checkEncoding #382

Job	Run time
ruby-versions / Generate Ruby versions	2s
windows-latest 2.7	3m 30s
windows-latest 3.0	1m 20s
windows-latest 3.1	1m 17s
windows-latest 3.2	49s
windows-latest 3.3	1m 16s
windows-latest 3.4	2m 16s
windows-latest jruby-head	1m 30s
windows-latest mingw	52s
windows-latest mswin	1m 4s
	13m 56s

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