[infra] Reject unexpected extra arguments in approve_results.

Change-Id: I441572d5e6d99aa3f3ff3427f8562fa417405d09
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/95643
Reviewed-by: William Hesse <whesse@google.com>

tools/approve_results.dart

@@ -305,6 +305,12 @@ ${parser.usage}""");
     return;
   }
 
+  if (options.rest.isNotEmpty) {
+    stderr.writeln("Unexpected extra argument: ${options.rest.first}");
+    exitCode = 1;
+    return;
+  }
+
   // Locate gsutil.py.
   gsutilPy =
       Platform.script.resolve("../third_party/gsutil/gsutil.py").toFilePath();