[emirmrkaljevic]

Refs #15533

nl passed the directory name to translate!, which hands number-like arguments to Fluent as numbers, so a directory called 007, 1e3, 2.50 or +5 was reported reformatted:

$ mkdir 007 1e3
$ nl 007 1e3            # GNU coreutils 9.12
nl: 007: Is a directory
nl: 1e3: Is a directory
$ ./target/debug/nl 007 1e3   # uutils main
nl: 7: Is a directory
nl: 1000: Is a directory

This switches the nl-error-is-directory call to translate_text!, as in #15534 (tail) and #15541 (tac). The other nl errors don't go through translate! with a file name, so they were already fine. The new test fails on main and passes with the change; output now matches GNU 9.12 for 007, 1e3, 2.50 and +5.

Found with behave, which recorded GNU's behaviour and replayed it against uutils.

[cakebaker]

Thanks!