id: mark passwd-format and pretty-print as conflicting

These are non-sensical to combine, and didn't work reasonably anyway.
Also, passwd-formatting is our own extension, so there is no need for
compatibility anyway.

tests/by-util/test_id.rs

@@ -461,3 +461,16 @@ fn test_id_no_specified_user_posixly() {
         }
     }
 }
+
+#[test]
+#[cfg(all(unix, not(target_os = "android")))]
+fn test_id_pretty_print_password_record() {
+    // `-p` is BSD only and not supported on GNU's `id`.
+    // `-P` is our own extension, and not supported by either GNU nor BSD.
+    // These must conflict, because they both set the output format.
+    new_ucmd!()
+        .arg("-p")
+        .arg("-P")
+        .fails()
+        .stderr_contains("the argument '-p' cannot be used with '-P'");
+}