fix: stop using _parse_known_args - use parse_known_args

after 3.14 there is change of signature in the function and those patches
are even picked up into debian 3.12 version thus breaking the code here,
and in effect disabling load of commands from extensions.  For a more
general fix on not picking up during early parsing failure:
datalad#7679

and the underlying issue: datalad#7678

datalad/cli/parser.py

@@ -98,11 +98,7 @@ def setup_parser(
         description=help_gist,
         formatter_class=formatter_class,
         add_help=False,
-        # TODO: when dropping support for Python 3.8: uncomment below
-        # and use parse_known_args instead of _parse_known_args:
-        # # set to False so parse_known_args does not add its error handling
-        # # Added while RFing from using _parse_known_args to parse_known_args.
-        # exit_on_error=False,
+        exit_on_error=False,
     )
 
     # common options
@@ -353,7 +349,7 @@ def single_subparser_possible(cmdlineargs, parser, completing):
     # Before doing anything additional and possibly expensive see may be that
     # we have got the command already
     try:
-        parsed_args, unparsed_args = parser._parse_known_args(
+        parsed_args, unparsed_args = parser.parse_known_args(
             cmdlineargs[1:], argparse.Namespace())
         # before anything handle possible datalad --version
         if not unparsed_args and getattr(parsed_args, 'version', None):