uv_sync_flags and tox 4.21 native toml configuration

[azmeuk]

I tested passing groups to uv_sync_flags with this configuration (with the new tox 4.21 native toml configuration support), as suggested in #113, but without success at the moment:

[tool.tox.env.doc]
runner = "uv-venv-lock-runner"
uv_sync_flags = ["--group=doc"]
commands = [
    ["sphinx-build", "--builder", "html", "doc", "build/sphinx/html"],
    ["sphinx-build", "--builder", "man", "doc", "build/sphinx/html"],
]

It fails with TypeError: '--group=doc' is not list.

When passing a simple string like uv_sync_flags = "--group=doc" it also fails with the same error message.

Originally posted by @azmeuk in #114 (comment)

[gaborbernat]

https://github.com/tox-dev/tox-uv/releases/tag/1.16.0 also now have support for dedicated field https://github.com/tox-dev/tox-uv#dependency_groups to be more unified with upstream tox

[azmeuk]

Thank you for the quick fix!