updates to latest alpine, maven plugins and JDK 21.0.4 #132

	# yamllint --format github .github/workflows/test.yml
	---
	name: test

	# We don't test documentation-only commits.
	on:
	# We run tests on non-tagged pushes to master that aren't a commit made by the release plugin
	push:
	tags: ''
	branches: master
	paths-ignore: '*/.md'
	# We also run tests on pull requests targeted at the master branch.
	pull_request:
	branches: master
	paths-ignore: '*/.md'

	jobs:
	test:
	name: test (${{ matrix.name }})
	runs-on: ubuntu-22.04 # newest available distribution, aka jellyfish
	strategy:
	fail-fast: false # don't fail fast as some failures are LTS specific
	matrix: # match with maven-enforcer-plugin rules in pom.xml
	include:
	- name: build-arg
	version: 21.0.4_p7
	- name: implicit
	version: master
	steps:
	- name: Checkout Repository
	uses: actions/checkout@v4
	with:
	fetch-depth: 1 # only needed to get the sha label
	# We can't cache Docker without using buildx because GH actions restricts /var/lib/docker
	# That's ok because DOCKER_PARENT_IMAGE is always ghcr.io and local anyway.
	- name: Test
	run: build-bin/configure_test && build-bin/test ${{ matrix.version }}

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