Use C++20 for programs that generate the HTML lists #69

	# A workflow to check generating the HTML lists works.
	# The pages generated by this will have incorrect "Last modified" dates
	# for the issues, because there is no meta-date/dates file used here.
	# That's OK, because this is just a quick check to ensure that the XML
	# is well-formed and the lists can be generated, suitable for checking
	# pull requests are OK to merge.

	name: Generate HTML issues for a pull request

	on:
	pull_request:
	branches: [ master ]

	jobs:
	build:
	runs-on: ubuntu-24.04

	steps:
	- uses: actions/checkout@v4
	with:
	fetch-depth: 1

	- name: Compile binary programs
	run: make CXX=g++-14 pgms

	- name: Extract issue timestamps from published files
	run: \|
	git fetch --depth=1 origin gh-pages
	git worktree add gh-pages FETCH_HEAD
	rm -f meta-data/dates
	for i in gh-pages/issue[0-9]*.html ; do
	n="${i#gh-pages/issue}" ; n="${n%.html}" ;
	date=`sed -n 's;^.*Last modified:</b> $....-..-..$</p>$;\1;p' $i`
	date "+$n %s" -d "$date" >> meta-data/dates
	done

	- name: Generate HTML lists
	run: make lists

	- name: Package changed files
	run: \|
	cp mailing/issue*.html gh-pages/
	mkdir html
	git -C gh-pages add issue*.html
	git -C gh-pages diff --cached --name-only \| while read f ; do
	cp gh-pages/$f html
	done

	- name: Upload new HTML files for inspection
	uses: actions/upload-artifact@v4
	with:
	name: pull-${{ github.event.number }}-html
	path: html/issue*.html
	retention-days: 7

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