feat: add GH action markdown linting for spec file #421

	name: validate-markdown

	# Author: @ralfhandl based on work of @MikeRalphson

	#
	# This workflow validates markdown files in the `versions` directory matching *.md
	#

	# run this on push to any branch and creation of pull-requests
	on: [push, pull_request]

	jobs:
	mdv:

	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v4 # checkout repo content
	with:
	fetch-depth: 0
	# - name: use the javascript environment from main
	# run: \|
	# git checkout remotes/origin/main -- package.json package-lock.json .markdownlint.yaml
	- uses: actions/setup-node@v4 # setup Node.js
	with:
	node-version: '20.x'
	- name: Validate markdown
	run: npx --yes mdv ./versions/[1-2].*.md
	- name: Lint markdown
	run: npx --yes markdownlint-cli --config .markdownlint.yaml versions/1.0.[^0].md versions/1.[1-9]..md versions/2..md

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