Github: introduce CI for OpenBSD. #3

	name: 'Moulti checks (OpenBSD)'
	on:
	- push
	jobs:
	openbsdchecks:
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4
	- name: OpenBSD
	uses: vmactions/openbsd-vm@v1
	with:
	usesh: true
	prepare: \|
	pkg_add python py3-pip bash
	run: \|
	set -e
	python3.11 --version
	pip --version
	python3.11 -m venv .venv
	. .venv/bin/activate
	pip install --upgrade pip
	# Remove problematic python packages:
	# - bpython: unnecessary, depends on greenlet and thus on a recent C++ compiler
	# - ruff: depends on a Rust compiler
	# - twine: unnecessary, depends on a Rust compiler
	sed -i '/bpython/d; /ruff/d; /twine/d' requirements.txt
	pip install -r requirements.txt
	# no ruff, no ruff check
	mypy src/moulti
	pylint src/moulti
	pip install -e .
	# This runs all tests except:
	# - test_diff_with_delta (requires delta 0.18.x)
	pytest -v

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