[BUG] PyPI maintainer is off

[niccokunzmann]

Describe the bug

If you go to https://pypi.org/project/icalendar/
You can see that
Betreuer: Christian Geier has the wrong email.

Expected behavior

All maintainers should be listed

This can be fixed in the pyproject.toml

Environment

• OS:
• Python version:
• icalendar version: 6.0.0

Additional context

• I tested it with the latest version pip3 install https://github.com/collective/icalendar.git
• I attached the ICS source file or there is no ICS source file

[niccokunzmann]

This is a problem of the build system.

Maintainer: Christian Geier
Maintainer-email: Nicco Kunzmann <niccokunzmann@rambler.ru>, Jaca <vitouejj@gmail.com>

What we do is correct:
https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#authors-maintainers

This is followed up here: pypa/hatch#1747