sort: allow -f to be pass multiple time

Fix #5667

tests/by-util/test_sort.rs

@@ -1181,3 +1181,11 @@ fn test_tmp_files_deleted_on_sigint() {
 fn test_same_sort_mode_twice() {
     new_ucmd!().args(&["-k", "2n,2n", "empty.txt"]).succeeds();
 }
+
+#[test]
+fn test_args_override() {
+    new_ucmd!()
+        .args(&["-f", "-f"])
+        .pipe_in("foo")
+        .succeeds();
+}