argparse exclusive argument group error unintelligible

Bug report

Bug description:

    import argparse
    import os.path
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "--debug",
        action="store_true",
        help="print out debugging information",
    )
    # Added optional branch argument
    parser.add_argument(
        "-b",
        "--branch",
        default="main",
        help="branch name to store commits in (default: main)",
    )
    parser.add_argument(
        "--non-interactive",
        action="store_true",
        help="disable interactive prompts for missing author information, pass --yes to lfs import",
    )
    parser.add_argument(
        "--template",
        default=os.path.join(
            os.path.dirname(__file__), "template"
        ),
        help="add files from this directory to every revision",
    )
    parser.add_argument(
        "--object-format",
        default="sha256",
        help="git object format to use (default: sha256)",
    )
    parser.add_argument(
        "--changelog",
        nargs="?",
        const=pkg_base,
        help="use changelog for commit messages, "
        f"package name is guessed ({pkg_base}) or can be specified",
    )
    repo_group = parser.add_mutually_exclusive_group(required=True)
    repo_group.add_argument(
        "--stdout",
        action="store_true",
        help="output git fast-import data to stdout",
    )
    repo_group.add_argument(
        "repository",
        nargs="?",
        help="import package into this git repository if --stdout is not given",
    )
    args = parser.parse_args()

$ python3 osc_fast_export.py 
usage: osc_fast_export.py [-h] [--debug] [-b BRANCH] [--non-interactive] [--template TEMPLATE]
                          [--object-format OBJECT_FORMAT] [--changelog [CHANGELOG]] (--stdout |
                          repository)
osc_fast_export.py: error: one of the arguments --stdout repository is required

The sentence

one of the arguments --stdout repository is required

is unintelligible. I wrote the code so I know why the output is like this but this is supposed to be read by a user who never looked at the code. The grammar of that sentence is broken.

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-157134

Start with the argparse mutually exclusive-group entry point shown in the report and reproduce the command with neither --stdout nor repository. Trace the resulting required-argument diagnostic and its existing coverage; done means the user-facing message is grammatical and clearly explains the requirement, with a regression test for this case.