tests/basics/sys1.py: Add test for calling sys.exit() without any args.

tests/basics/sys1.py

@@ -24,6 +24,11 @@ try:
 except SystemExit as e:
     print("SystemExit", e.args)
 
+try:
+    sys.exit()
+except SystemExit as e:
+    print("SystemExit", e.args)
+
 try:
     sys.exit(42)
 except SystemExit as e: