chmod: Fix chmod -c --reference reporting when no change is made (#6016)

* Make fperm hold 6 digit octal permission. Set it to 4 digits when displaying

* Add test

* Make every permission 4 octal digits

* Change test name to be more suggestive

* chmod: merge two args in test

---------

Co-authored-by: Daniel Hofstetter <daniel.hofstetter@42dh.com>

tests/by-util/test_chmod.rs

@@ -645,6 +645,20 @@ fn test_quiet_n_verbose_used_multiple_times() {
         .succeeds();
 }
 
+#[test]
+fn test_changes_from_identical_reference() {
+    let scene = TestScenario::new(util_name!());
+    let at = &scene.fixtures;
+    at.touch("file");
+    scene
+        .ucmd()
+        .arg("-c")
+        .arg("--reference=file")
+        .arg("file")
+        .succeeds()
+        .no_stdout();
+}
+
 #[test]
 fn test_gnu_invalid_mode() {
     let scene = TestScenario::new(util_name!());