Attempt to fix CI failures related to PyYAML. #692

	on: pull_request

	jobs:
	validate:
	name: Validate build
	runs-on: ubuntu-latest
	container: python:3
	steps:
	- uses: actions/checkout@v1
	with:
	fetch-depth: 1
	- name: Install pre-requisites
	run: pip install -r requirements.txt
	- name: Build
	run: mkdocs build -v --clean

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