Migrate to ESLint 9 and ESLint flat config #4142

	name: Continuous integration
	on: [push]
	jobs:
	ci:
	runs-on: ubuntu-latest
	steps:
	- name: Checkout
	uses: actions/checkout@v4
	- name: Cache the node_modules dir
	uses: actions/cache@v4
	with:
	path: node_modules
	key: ${{ runner.os }}-node_modules-${{ hashFiles('yarn.lock') }}
	- name: Install
	run: yarn install --immutable
	- name: Format
	run: yarn checkformatting
	- name: Lint
	run: yarn lint
	- name: Typecheck
	run: yarn typecheck
	- name: Test
	run: yarn test
	- name: Upload coverage to Codecov
	uses: codecov/codecov-action@v4
	with:
	files: ./coverage/coverage-final.json
	token: ${{ secrets.CODECOV_TOKEN }}

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