Use whoami's own uucore locale in the whoami command (#19144)

## Description
`whoami` sets up uutils' error translations with
`localized_help_template("touch")`, so it loads `touch`'s translations
instead of `whoami`'s. Any `uu_whoami` error message ID would then be
looked up in the wrong translations and could show up as a raw ID. This
PR passes `"whoami"`, like the other uutils-backed commands (`mktemp`,
`mv`, `cp`, `mkdir`, `touch`, `uname`) already do for their own utils.

This is the nushell-side fix I mentioned in #19004. The main cause of
that issue (uucore keeping whichever util's translations loaded first)
is upstream and tracked in uutils/coreutils#15040.

## User-facing changes (Release notes)
- Fixed `whoami` loading translations for the wrong command, which could
make its error messages show up untranslated.

## Additional notes
Related #19004

crates/nu-command/src/platform/whoami.rs

@@ -33,7 +33,7 @@ impl Command for Whoami {
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         // setup the uutils error translation
-        let _ = localized_help_template("touch");
+        let _ = localized_help_template("whoami");
 
         let output = match uu_whoami::whoami() {
             Ok(username) => username.to_string_lossy().to_string(),