Refactor PHPUnit GitHub workflow for simplicity

The PHPUnit GitHub workflow was significantly simplified by reducing the amount of work done in the YAML file. The previous workflow was manually setting up the test environment (downloading WordPress, setting up MySQL, etc.) within this file.

The updated workflow uses a custom GitHub action that handles these setup steps, resulting in a cleaner and easier to read workflow file.

Moreover, the PHP versions and WordPress version for testing have been updated to reflect more current versions.

.github/workflows/phpunit.yml

@@ -1,51 +1,16 @@
-name: Unit Tests
+name: Testing Suite
+
 on:
   pull_request:
-  workflow_dispatch:
+
 jobs:
-  tests:
-    name: "PHP: ${{ matrix.php }} (MU: ${{ matrix.multisite }})"
-    runs-on: ubuntu-latest
+  php-tests:
     strategy:
-      fail-fast: true
       matrix:
-        multisite: [0, 1]
-        php: ['8.0', '7.4', '7.3', '7.2', '7.1']
-    env:
-      WP_CORE_DIR: /tmp/wordpress/
-      WP_MULTISITE: ${{ matrix.multisite }}
-    services:
-      mysql:
-        image: mysql:5.7
-        env:
-          MYSQL_ALLOW_EMPTY_PASSWORD: yes
-        ports:
-          - 3306:3306
-        options: --health-cmd="mysqladmin ping" --health-interval=10s --health-timeout=5s --health-retries=3
-    steps:
-      - name: Cancel Previous Runs
-        uses: styfle/[email protected]
-        with:
-          all_but_latest: true
-      - name: Checkout code
-        uses: actions/checkout@v3
-      - name: Setup PHP
-        uses: shivammathur/setup-php@v2
-        with:
-          php-version: ${{ matrix.php }}
-          extensions: dom, curl, libxml, mbstring, zip, pcntl, pdo, sqlite, pdo_sqlite, gd
-          coverage: none
-      - name: Install dependencies
-        uses: ramsey/composer-install@v2
-      - name: Set up WordPress
-        run: |
-          bash <(curl -s "https://raw.githubusercontent.com/wp-cli/sample-plugin/master/bin/install-wp-tests.sh") wordpress_unit_tests root '' 127.0.0.1
-          rm -rf "${WP_CORE_DIR}wp-content/plugins"
-          mkdir -p "${WP_CORE_DIR}wp-content/plugins/publish-to-apple-news"
-          rsync -a --exclude=.git . "${WP_CORE_DIR}wp-content/plugins/publish-to-apple-news"
-          cd ${WP_CORE_DIR}wp-content/plugins/publish-to-apple-news && composer install
-      - name: Run tests
-        shell: bash
-        run: |
-          cd ${WP_CORE_DIR}/wp-content/plugins/publish-to-apple-news
-          composer run phpunit
+        php: ['8.2', '8.1', '8.0', '7.4']
+        wordpress: ["latest"]
+    uses: alleyinteractive/.github/.github/workflows/php-tests.yml@main
+    with:
+      command: "test"
+      php: ${{ matrix.php }}
+      wordpress: ${{ matrix.wordpress }}