argparse: space in an incorrect argument adds it to nargs="*", instead of raising an error

[abcydybcy]

Bug report

Bug description:

Code to recreate:

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("args", nargs="*")
print(parser.parse_args())

Current behaviour:
If the wrong argument contains a space, it is added to the catch-all arguments:

> python bug.py --wrong-arg="foo bar"
Namespace(args=['--wrong-arg=foo bar'])

But if it doesn't contain a space, expected behaviour happens:

> python bug.py --wrong-arg="foobar" 
usage: bug.py [-h] [args ...]
bug.py: error: unrecognized arguments: --wrong-arg=foobar

Expected behaviour:
Calling this program as bug.py --wrong-argument="foo bar" prints an error message:

usage: bug.py [-h] [--name NAME] [args ...]
bug.py: error: unrecognized arguments: --wrong-arg=foo bar.

CPython versions tested on:

3.11

Operating systems tested on:

No response

[hugovk]

Thanks for the report, this looks like a duplicate of #66623.