bpo-41255: handle argparse errors with exit_on_error=False consistently

[joshmeranda]

bpo-41255

When unknown arguments are passed to parse_args or required arguments not passed to either parse_args or parse_known_args argpase exits despite exit_on_error=False. This is not very intuitive, instead any error parsing arguments should result in an ArgumentError which can be handled by the user.

https://bugs.python.org/issue41255

[the-knights-who-say-ni]

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[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[MaxwellDupre]

Works for me:
Ran 1658 tests in 2.516s
OK

Simple bug mentioned case too!
Nice work

[AA-Turner]

Trigger CLA.

A

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[serhiy-storchaka]

Thank you for your contribution @joshmeranda. I apologize for the fact that this PR was neglected for a long time. The problem has already been solved in another way.