Add pytest-xdist to speed up test suite

[joshuadavidthomas]

pytest-xdist helps speed up test execution by distribution tests across multiple CPUs. After installing pytest-xdist in the venv, I got a 78% decrease in the test suite run time, from 4 min 18 sec down to 1 min 52 sec.

Before

$ pytest
================================ test session starts ================================
platform linux -- Python 3.12.0, pytest-7.4.4, pluggy-1.4.0
django: version: 4.1.13, settings: siteroot.settings.dev (from ini)
rootdir: /home/josh/projects/linkding
configfile: pytest.ini
plugins: django-4.7.0
collected 545 items

...

=================== 545 passed, 103 warnings in 258.02s (0:04:18) ===================

After

$ python -m pip install pytest-xdist
Collecting pytest-xdist
  Downloading pytest_xdist-3.5.0-py3-none-any.whl.metadata (3.1 kB)
Collecting execnet>=1.1 (from pytest-xdist)
  Using cached execnet-2.0.2-py3-none-any.whl.metadata (2.9 kB)
Requirement already satisfied: pytest>=6.2.0 in /home/josh/.pyenv/versions/linkding-3.12/lib/python3.12/site-packages (from pytest-xdist) (7.4.4)
Requirement already satisfied: iniconfig in /home/josh/.pyenv/versions/linkding-3.12/lib/python3.12/site-packages (from pytest>=6.2.0->pytest-xdist) (2.0.0)
Requirement already satisfied: packaging in /home/josh/.pyenv/versions/linkding-3.12/lib/python3.12/site-packages (from pytest>=6.2.0->pytest-xdist) (23.2)
Requirement already satisfied: pluggy<2.0,>=0.12 in /home/josh/.pyenv/versions/linkding-3.12/lib/python3.12/site-packages (from pytest>=6.2.0->pytest-xdist) (1.4.0)
Using cached pytest_xdist-3.5.0-py3-none-any.whl (42 kB)
Using cached execnet-2.0.2-py3-none-any.whl (37 kB)
Installing collected packages: execnet, pytest-xdist
Successfully installed execnet-2.0.2 pytest-xdist-3.5.0

$ pytest -n auto
================================ test session starts ================================
platform linux -- Python 3.12.0, pytest-7.4.4, pluggy-1.4.0
django: version: 4.1.13, settings: siteroot.settings.dev (from ini)
rootdir: /home/josh/projects/linkding
configfile: pytest.ini
plugins: xdist-3.5.0, django-4.7.0
8 workers [545 items]

...

=================== 545 passed, 125 warnings in 112.78s (0:01:52) ===================

[sissbruecker]

Open to this, assuming the current test suite passes with it.