Change usage of `numeric_version()`

[jennybc]

From CRAN 2023-06-19:

A recent PR (https://bugs.r-project.org/show_bug.cgi?id=18548) showed
that whereas version inputs to numeric_version() et al were always
documented to be "suitable character vectors" (or numeric vesion
objects), the implementation also accepted numeric inputs via
as.character() coercion, the results of which however are (at least
currently) dependent on the setting of the OutDec option. We are
currently discussing the best way forward.

Meanwhile, can you please change your code to use character instead of
numeric inputs? Grepping and code analysis finds

 ./usethis/R/release.R:    return(numeric_version(0))

Please fix as quickly as possible.

I said I would do a patch release within a week.