fix: correct pluralization in the non-import reference warning

Live smoke printed 'reference s to moved files' (the plural 's' was
separated from the noun by the format placeholder). The e2e now pins
the exact warning text.

tests/cli_refs.rs

@@ -47,7 +47,7 @@ fn human_dry_run_warns_on_stderr_and_exits_zero() {
     jmove(&tmp, &["mv", "lib/sum.ts", "lib/total.ts", "--dry-run"])
         .success()
         .stderr(
-            predicate::str::contains("non-import reference")
+            predicate::str::contains("3 non-import references to moved files")
                 .and(predicate::str::contains("README.md:1"))
                 .and(predicate::str::contains("__tests__/sum.test.ts:1")),
         );