Use python3.9 in CI (#599) #6

	name: code-format-check

	on:
	# code format check for pull requests and the dev branch
	push:
	branches:
	- dev
	pull_request:

	concurrency:
	# automatically cancel the previously triggered workflows when there's a newer version
	group: build-${{ github.event.pull_request.number \|\| github.ref }}
	cancel-in-progress: true

	jobs:
	flake8-py3:
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v2
	- name: Set up Python 3.9
	uses: actions/setup-python@v2
	with:
	python-version: 3.9
	- name: cache weekly timestamp
	id: pip-cache
	run: \|
	echo "::set-output name=datew::$(date '+%Y-%V')"
	- name: cache for pip
	uses: actions/cache@v2
	id: cache
	with:
	path: ~/.cache/pip
	key: ${{ runner.os }}-pip-${{ steps.pip-cache.outputs.datew }}
	- name: Install dependencies
	run: \|
	python -m pip install --upgrade pip wheel
	python -m pip install -r requirements-dev.txt
	- name: type check
	run: \|
	# clean up temporary files
	$(pwd)/runtests.sh --clean
	# Git hub actions have 2 cores, so parallize pytype
	$(pwd)/runtests.sh --codeformat -j 2

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