Bump actions/checkout from 3 to 4 #768

	# Test run with no optional dependencies installed, to help
	# detect any accidental dependencies.

	name: Core tests

	on:
	pull_request

	jobs:
	core:
	strategy:
	matrix:
	os: [ubuntu-latest, windows-latest]
	python-version: ['3.8', '3.9', '3.10', '3.11', '3.12', '3.13']

	runs-on: ${{ matrix.os }}

	steps:
	- uses: actions/checkout@v4
	- name: Set up Python ${{ matrix.python-version }}
	uses: actions/setup-python@v4
	with:
	python-version: ${{ matrix.python-version }}
	allow-prereleases: true
	- name: Install local package
	run: \|
	# Uninstall setuptools so that the tests will catch any accidental
	# dependence of the Traits source on setuptools. Note that in future
	# setuptools may not exist in a newly-created venv
	# https://github.com/python/cpython/issues/95299
	python -m pip uninstall -y setuptools
	python -m pip install .
	python -m pip list
	- name: Test Traits package
	run: \|
	mkdir testdir
	cd testdir
	python -m unittest discover -v traits

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