[libpng18] [build system] Require ISO-C when building libpng #139

	name: Linting libpng

	on:
	push:
	branches:
	- libpng16
	- libpng18
	pull_request:
	branches:
	- libpng16
	- libpng18

	jobs:
	lint:
	runs-on: ubuntu-latest
	timeout-minutes: 5
	steps:
	- name: Set up the cache
	uses: actions/cache@v4
	with:
	path: ~/.cache/pip
	key: ${{ runner.os }}-pip-${{ hashFiles('**/pip.txt') }}
	restore-keys: ${{ runner.os }}-pip-
	- name: Install yamllint
	run: pip install yamllint
	- name: Check out the code
	uses: actions/checkout@v4
	- name: Run the linting script
	run: bash ./ci/ci_lint.sh

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