[self-tests] tests fail against setuptools 80.9.0

[stanislavlevin]

https://setuptools.pypa.io/en/stable/history.html#v80-9-0

Set a deadline for the removal of pkg_resources later this year (December). (#3085)

and emits corresponding warning.

This leads to test failure:

=================================== FAILURES ===================================
_______ AstroidManagerTest.test_identify_old_namespace_package_protocol ________

self = <tests.test_manager.AstroidManagerTest testMethod=test_identify_old_namespace_package_protocol>

    def test_identify_old_namespace_package_protocol(self) -> None:
        # Like the above cases, this package follows the old namespace package protocol
        # astroid currently assumes such packages are in sys.modules, so import it
        # pylint: disable-next=import-outside-toplevel
>       import tests.testdata.python3.data.path_pkg_resources_1.package.foo as _  # noqa

tests/test_manager.py:124: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
tests/testdata/python3/data/path_pkg_resources_1/package/__init__.py:5: in <module>
    __import__("pkg_resources").declare_namespace(__name__)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

...

E   UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.

/usr/lib64/python3/site-packages/pkg_resources/__init__.py:98: UserWarning