Adding additional potential systemctl exit status for Ubuntu 24

[pfuntner]

This is a simple change to SystemdService.is_running() to allow it to work for Ubuntu 24 to correct the symptoms in #775.

On Ubuntu 24, systemctl is-activate foobar (assuming foobar is an unknown service) has an exit status of 4 but the is_running() method only expects exit status values of 0, 1, or 3. My change just allows an exit status of 4 as well. The method will return False anyway but it won't raise the AssertionError.

I was following CONTRIBUTING.rst and tried running tox from a virtual environment on my development machine but it failed and I'm not sure how to fix it. Here's the output: tox output.txt.

[pfuntner]

It looks like the tox tests were run automatically on the Github side. I didn't expect my tiny change would introduce a problem and I see it worked. 🥳

[martinhoyer]

There is already #773, just no reviewers it seems :(

[pfuntner]

There is already #773, just no reviewers it seems :(

Oh, great. Thanks, I'll close this one.