gh actions: pin OS version, update checkout action version #38

	name: Build and release PDF

	on: push

	jobs:
	pdf:
	runs-on: ubuntu-22.04

	container:
	image: texlive/texlive

	steps:
	- name: checkout
	uses: actions/checkout@v4

	- name: build
	run: \|
	sh .github/scripts/build_pdf.sh built_pdfs

	# Upload artifact for each CI run. Not needed for release_if_tag! This
	# uses the output of steps.build .
	- name: upload artifact
	uses: actions/upload-artifact@master
	with:
	name: built_pdfs
	path: built_pdfs

	# Create a release and attach built_pdfs/*.pdf to that for easy download.
	- name: release_if_tag
	uses: softprops/action-gh-release@master
	if: startsWith(github.ref, 'refs/tags/')
	with:
	files: "built_pdfs/*"
	env:
	GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

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