Autodoc parameter types in parameter list not resolving for TypeVar or aliases

Describe the bug

When specifying code like:

from __future__ import annotations

from typing import Generic, TypeVar, Union

#: A variable
X = Union[str, int]

#: Another variable
Y = TypeVar("Y")

class Z:
    """A class we pass as an arg"""

class Bar(Generic[Y]):
    """The class we want
    
    :param X x: an arg
    :param Y y: another arg
    :param Z z: a third arg
    """

    def __init__(self, x: X, y: Y, z: Z) -> None:
        self.x = x
        self.y = y
        self.z = z

    def foo(self) -> Y:
        return self.y

The parameter z or Bar.__init__ is linked correctly in both the signature and the parameter list, but x and y are not resolved in the parameter list.

The console output is:

<unknown>:1: WARNING: py:obj reference target not found: typing.Union
sphinx-autodoc-types-issue-demo/mycode.py:docstring of mycode.Bar:: WARNING: py:class reference target not found: X
sphinx-autodoc-types-issue-demo/mycode.py:docstring of mycode.Bar:: WARNING: py:class reference target not found: Y

How to Reproduce

$ git clone https://github.com/thomascobb/sphinx-autodoc-types-issue-demo.git
$ cd sphinx-autodoc-types-issue-demo
$ pip sphinx
$ sphinx-build docs html
$ firefox html/index.html

Expected behavior

I would like to see the links for x and y to appear like that of z in the parameter list of Bar, linking to the aliases defined further up the docs

Your project

https://github.com/thomascobb/sphinx-autodoc-types-issue-demo

Screenshots

NOTE X and Y in the parameter list (black) have no links, while Z (blue) has correctly generated a link

OS

Linux

Python version

3.7

Sphinx version

4.2.0

Sphinx extensions

sphinx.ext.autodoc

Extra tools

firefox

Additional context

No response

Reproduce the issue with the sphinx-autodoc-types-issue-demo project, using docs, mycode.py, and the sphinx.ext.autodoc extension. Inspect how autodoc resolves parameter-list types for the X alias and Y TypeVar, then verify that both links appear like the existing Z link without the reported warnings.