markdownlint-cli2, pin bundler, drop node 16, add node 21 #15

	name: Build & Release

	on:
	push:
	branches: [main]
	pull_request:
	branches: [main]

	env:
	REGISTRY: ghcr.io

	jobs:
	build_release:
	permissions: write-all
	name: "Build and Release"
	strategy:
	matrix:
	VERSIONS: [ {ruby: 2.7.3, ghpages: 226}, {ruby: 2.7.4, ghpages: 228}]
	NODE_MAJOR_VERSION: [18,20,21]
	runs-on: ubuntu-latest
	env:
	RUBY_VERSION: ${{ matrix.VERSIONS.ruby }}
	NODE_MAJOR_VERSION: ${{ matrix.NODE_MAJOR_VERSION }}
	GITHUB_PAGES_VERSION: ${{ matrix.VERSIONS.ghpages }}

	steps:
	- name: Lowercase repo for IMAGE_NAME
	run: \|
	echo "IMAGE_NAME=${GITHUB_REPOSITORY,,}" >>${GITHUB_ENV}
	- uses: actions/checkout@v3
	- name: Build the Docker image
	run: docker build . --file Dockerfile --tag ${REGISTRY}/${IMAGE_NAME}:ruby${RUBY_VERSION}-node${NODE_MAJOR_VERSION} --build-arg RUBY_VERSION=${RUBY_VERSION} --build-arg NODE_MAJOR_VERSION=${NODE_MAJOR_VERSION} --build-arg BUILD_DATE=$(date -u +%Y-%m-%d_%H-%M-%S) --build-arg VCS_REF=${GITHUB_SHA} --build-arg GH_PAGES_VERSION=${GITHUB_PAGES_VERSION} --progress=plain
	- name: Inspect the built image
	run: docker inspect ${REGISTRY}/${IMAGE_NAME}:ruby${RUBY_VERSION}-node${NODE_MAJOR_VERSION}
	- name: Login to registry (non-PR only)
	if: github.event_name != 'pull_request'
	uses: docker/login-action@v2.0.0
	with:
	registry: ${{ env.REGISTRY }}
	username: ${{ github.actor }}
	password: ${{ secrets.GITHUB_TOKEN }}
	- name: Push Container to registry (non-PR only)
	if: github.event_name != 'pull_request'
	run: docker push --all-tags ${REGISTRY}/${IMAGE_NAME}

Provide feedback