Moves from JDK 15 to LTS version 17 #22

	# yamllint --format github .github/workflows/test.yml
	---
	name: test webmvc4-boot

	on:
	# We deploy non-tagged pushes to master relevant for this project. We can't opt out of
	# documentation-only commits because GH actions does not permit paths and paths-ignore.
	pull_request:
	branches: master
	paths:
	- "build-bin/**"
	- "docker/**"
	- "webmvc4-boot/**"
	- ".github/workflows/test-webmvc4-boot.yaml"
	- "parent-pom.xml"

	jobs:
	test:
	runs-on: ubuntu-20.04 # newest available distribution, aka focal
	steps:
	- name: Checkout Repository
	uses: actions/checkout@v2
	with:
	fetch-depth: 1
	- name: Cache local Maven repository
	uses: actions/cache@v2
	with:
	path: ./m2repository # Shared with the Docker build context via .dockerignore
	key: ${{ runner.os }}-webmvc4-boot-maven-${{ hashFiles('parent-pom.xml', 'webmvc4-boot/pom.xml') }}
	restore-keys: ${{ runner.os }}-webmvc4-boot-maven-
	# 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 webmvc4-boot
	run: \|
	build-bin/configure_test webmvc4-boot &&
	build-bin/test webmvc4-boot

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