test: Fix correct cli option value casting

Since we can set the type of the relevant option in the OPTIONS dict, we
should also let the cli correctly cast them on parsing, just as the env
options do.

topen.py

@@ -295,6 +295,7 @@ you view the task.
             dest=key,
             metavar=opt.metavar,
             help=opt.help_text,
+            type=opt.cast or str,
             default=None,
         )
     args = parser.parse_args()