Active support of Python 3.7 has ended in June 2020. Security support
has ended in June 2023.

The "pyproject" extra dependency has been removed from isort 5.0.0,
which has been released in July 2020. It caused a warning with when a
more recent version was installed:

    $ pip install -r requirements_dev.txt
    [...]
    WARNING: isort 5.13.2 does not provide the extra 'pyproject'
    [...]

We maintained non-obvious code to support versions of Git that did not
have the `--only-matching` option, which appeared in Git 2.19. This
version was released in September 2018, it's time to move on.

That's where all tools are configured (except ReadTheDocs, which does
not support `pyproject.toml`).

These checks seem useful, I don't know why they should disabled.

It was not necessary with Python >= 3.11, which ships with the
`tomllib` package in the standard library.

Also, the extra requirement could be a bit confusing, especially for
non-Python developers. "Do I need it now, will I need it later?"

For the sake of simplicity, the extra requirement has been removed.
We now always install `toml` on Python versions earlier than 3.11 (and
never on 3.11 and above).