How can I make sure that tests are not running in the same worker when using pytest-xdist?

Question

Imagine the following 5 tests:

from time import sleep

import pytest


@pytest.mark.xdist_group(name="group1")
def test_a() -> None:
    assert True


@pytest.mark.xdist_group(name="group1")
def test_b() -> None:
    assert True


def test_c() -> None:
    sleep(100000000000)
    assert True


def test_d() -> None:
    sleep(100000000000)
    assert True


def test_e() -> None:
    assert True

With this setup, test_a and test_b would run in the same worker.

Because test_c and test_d are long running tests, I want to make sure that they run in two different workers (if possible, ie, if more than 1 worker exists, otherwise, they should run in the only existing worker). I don't care where test_e runs.

Is there any way of accomplishing this?