warn on unused arguments in standardize_case_names()

[JanMarvin]

At least a warning is returned

library(openxlsx2)
xlsxFile <- system.file("extdata", "openxlsx2_example.xlsx", package = "openxlsx2")
wb1 <- wb_load(xlsxFile)

wb_to_df(wb1, colNames = FALSE, foo = TRUE)
#> Warning in standardize_case_names(...): unused arguments (foo)
#>        B    C  D     E     F          G            H       I        J
#> 2     NA Var2 NA  Var3  Var4       Var5         Var6    Var7     Var8
#> 3   TRUE    1 NA     1     a 2023-05-29 3209324 This #DIV/0! 01:27:15
#> 4   TRUE <NA> NA #NUM!     b 2023-05-23         <NA>       0 14:02:57
#> 5   TRUE    2 NA  1.34     c 2023-02-01         <NA> #VALUE! 23:01:02
#> 6  FALSE    2 NA  <NA> #NUM!       <NA>         <NA>       2 17:24:53
#> 7  FALSE    3 NA  1.56     e       <NA>         <NA>    <NA>     <NA>
#> 8  FALSE    1 NA   1.7     f 2023-03-02         <NA>     2.7 08:45:58
#> 9     NA <NA> NA  <NA>  <NA>       <NA>         <NA>    <NA>     <NA>
#> 10 FALSE    2 NA    23     h 2023-12-24         <NA>      25     <NA>
#> 11 FALSE    3 NA  67.3     i 2023-12-25         <NA>       3     <NA>
#> 12    NA    1 NA   123  <NA> 2023-07-31         <NA>     122     <NA>