Work around changes to argparse private API (#673)

Unfortunately, achieving colcon's arbitrary argument parsing involves
reaching into argparse private API. There was recently a change to that
API which was backported to stable Python releases, and this change is
necessary to restore the desired behavior.

colcon_core/command.py

@@ -261,9 +261,13 @@ def _parse_optional(self, arg_string):
             # the option.  As of that PR (which is in Python 3.13, and
             # backported to Python 3.12), it returns a 4-tuple.  Check for
             # either here.
+            # A similar regression later occurred when _parse_optional()
+            # started returning a list of tuples, brought in by
+            # https://github.com/python/cpython/pull/124631 .
             if result in (
                 (None, arg_string, None),
                 (None, arg_string, None, None),
+                [(None, arg_string, None, None)],
             ):
                 # in the case there the arg is classified as an unknown 'O'
                 # override that and classify it as an 'A'