Upgrade `actions/checkout` from `v2` to `v4`. #892

	name: tests

	on:
	push:
	branches: [ main ]
	pull_request:
	branches: [ main ]
	workflow_dispatch:
	inputs:
	git-ref:
	description: Git Ref (Optional)
	required: false

	jobs:
	build:
	runs-on: ubuntu-latest
	env:
	TEST_TMPDIR: '/tmp'
	strategy:
	matrix:
	python-version: ["3.11", "3.12"]
	steps:
	- uses: actions/checkout@v4

	- name: Set up Python ${{ matrix.python-version }}
	uses: actions/setup-python@v5
	with:
	python-version: ${{ matrix.python-version }}

	- name: Install dependencies
	run: \|
	pip install --upgrade pip setuptools
	python setup.py install
	pip install .[testing]

	- name: Run tests
	run: \|
	# Find all test files, print their names and execute them in parallel
	# with a maximum of 20 proccesses.
	find . -type f -name "*_test.py" -print0 \| xargs -t -0 -n1 -P 20 python3

Provide feedback