add kill list final new line test

tests/by-util/test_kill.rs

@@ -56,6 +56,14 @@ fn test_kill_list_all_signals() {
         .stdout_contains("HUP");
 }
 
+#[test]
+fn test_kill_list_final_new_line() {
+    new_ucmd!()
+        .arg("-l")
+        .succeeds()
+        .stdout_matches(&Regex::new("\\n$").unwrap());
+}
+
 #[test]
 fn test_kill_list_all_signals_as_table() {
     // Check for a few signals.  Do not try to be comprehensive.