workbook show error with multibyte string

[junpei-n]

When the length of a sheetname is larger than 20 and it is a multibyte string, XLSX.readxlsx raises StringIndexError.

julia>  
       using XLSX
       f = "sample.xlsx"
       
       XLSX.readxlsx(f)

XLSXFile("sample.xlsx") containing 18 Worksheets
            sheetname size          range        
-------------------------------------------------
ERROR: StringIndexError: invalid index [20], valid nearby indices [19]=>'日', [22]=>'本'

The bug, at workbook.jl#L76, can be fixed like

        name = s.name |> x -> length(x) > 20 ? join(collect(x)[1:20])*"…" : x
        # x[collect(eachindex(x))[1:20]] may be better

, however, it would print an undesired length string like

            sheetname size          range        
-------------------------------------------------
あいうえおかきくけこさしすせそなにぬねの_2022… 133x34        B1:AI133