Bump withr dependency to 2.5.0 and use local_tempfile(lines = ) in tests

This is a convenient improvement to `local_tempfile()` that's available since withr 2.5.0 on CRAN since March. By the time we release again, it should be mature enough that we are happy to depend on it.

_Originally posted by @MichaelChirico in https://github.com/r-lib/lintr/pull/1403#discussion_r900374747_