[config](build): downgrade to ubuntu-20.04(see if that fixes Ruby bui… #3234

	name: readme-checker.yml – Checks for suggested markdown
	on: [push, pull_request]

	permissions:
	contents: read

	jobs:
	lint:
	runs-on: ubuntu-latest
	steps:
	- name: Harden Runner
	uses: step-security/harden-runner@c95a14d0e5bab51a9f56296a4eb0e416910cd350 # v2.10.3
	with:
	egress-policy: audit

	- name: Checkout
	uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
	- name: Checking markdown
	uses: DavidAnson/markdownlint-cli2-action@05f32210e84442804257b2a6f20b273450ec8265 # v19.1.0
	with:
	globs: \|
	*.md
	*/.md
	!test/*.md

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