Revert to phpunit ^5.7.0 and limit test matrix to PHP 5.6-7.4 #4

	name: CI

	on: [push, pull_request]

	permissions:
	contents: read

	jobs:
	CI:
	runs-on: ubuntu-latest

	strategy:
	matrix:
	php:
	- '5.6'
	- '7.1'
	- '7.2'
	- '7.3'
	- '7.4'

	steps:
	- uses: actions/checkout@v4
	with:
	fetch-depth: 2

	- name: Setup PHP
	uses: shivammathur/setup-php@2.30.4
	with:
	php-version: ${{ matrix.php }}
	extensions: mbstring
	coverage: none

	- name: Install Dependencies
	run: composer update --no-interaction --prefer-dist

	- name: Run Tests
	run: composer run test

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