tests: pytest does not like return True from a test

tests: pytest does not like return True from a test

From running the test:
bgp_remove_private_as/test_bgp_remove_private_as.py::test_bgp_remove_private_as
  /home/sharpd/.local/lib/python3.10/site-packages/_pytest/python.py:198: PytestReturnNotNoneWarning: Expected None, but bgp_remove_private_as/test_bgp_remove_private_as.py::test_bgp_remove_private_as returned True, which will be an error in a future version of pytest.  Did you mean to use `assert` instead of `return`?
    warnings.warn(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

Signed-off-by: Donald Sharp <sharpd@nvidia.com>