[good first issue][BUG] Wrong type annotations in `PythonPathPackageWithDeps.__init__()`

[webknjaz]

I've hit this while looking into the plugins API and needed to extract some env deps.

Apparently, https://github.com/tox-dev/tox/blob/5e0784a/src/tox/tox_env/python/package.py#L33 claims that the PythonPathPackageWithDeps.deps attribute is a sequence of packages. But in reality, in runtime, it's a list of requirements. Also, the deps argument to the initializer gets a list of requirements too.

The correct argument signature would be deps: Sequence[Requirement] and the attribute assignment does not need to re-define it to something else to fool MyPy.

[marcosboger]

If no one working on this, I volunteer to pick it up. Besides fixing the type hint (as example below), would there be any other change needed?

class PythonPathPackageWithDeps(PathPackage):
    def __init__(self, path: Path, deps: Sequence[Requirement]) -> None:
        super().__init__(path=path)
        self.deps: Sequence[Requirement] = deps