mktemp: match GNU error message on too many args

Update the usage message when too many template arguments are given on
the command line to match that of GNU mktemp:

    mktemp: too many templates
    Try 'mktemp --help' for more information.

This fixes the test case `too-many` in the GNU test suite file
`tests/misc/mktemp.pl`.

src/uu/mktemp/src/mktemp.rs

@@ -10,7 +10,7 @@
 
 use clap::{crate_version, Arg, ArgMatches, Command};
 use uucore::display::{println_verbatim, Quotable};
-use uucore::error::{FromIo, UError, UResult};
+use uucore::error::{FromIo, UError, UResult, UUsageError};
 use uucore::format_usage;
 
 use std::env;
@@ -327,7 +327,15 @@ impl Params {
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     let args = args.collect_lossy();
 
-    let matches = uu_app().try_get_matches_from(&args)?;
+    let matches = match uu_app().try_get_matches_from(&args) {
+        Ok(m) => m,
+        Err(e) => {
+            if e.kind == clap::error::ErrorKind::TooManyValues && e.info[0] == "<template>..." {
+                return Err(UUsageError::new(1, "too many templates"));
+            }
+            return Err(e.into());
+        }
+    };
 
     // Parse command-line options into a format suitable for the
     // application logic.

tests/by-util/test_mktemp.rs

@@ -613,7 +613,11 @@ fn test_too_few_xs_suffix_directory() {
 
 #[test]
 fn test_too_many_arguments() {
-    new_ucmd!().args(&["-q", "a", "b"]).fails().code_is(1);
+    new_ucmd!()
+        .args(&["-q", "a", "b"])
+        .fails()
+        .code_is(1)
+        .usage_error("too many templates");
 }
 
 #[test]