Update CI php matrix

.github/workflows/continuous-integration.yml

@@ -0,0 +1,45 @@
+name: "Continuous Integration"
+
+on:
+  push:
+  pull_request:
+  schedule:
+    - cron: '0 0 * * *'
+
+jobs:
+  phpunit:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: true
+      matrix:
+        php: [8.0, 8.1]
+        stability: [prefer-stable]
+
+    name: PHP ${{ matrix.php }} - ${{ matrix.stability }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          extensions: dom, curl, libxml, mbstring, zip, pcntl, pdo, sqlite, pdo_sqlite, gd, memcached
+          tools: composer:v2
+          coverage: none
+
+      - name: Setup Memcached
+        uses: niden/actions-memcached@v7
+
+      - name: Install dependencies
+        uses: nick-invision/retry@v1
+        with:
+          timeout_minutes: 5
+          max_attempts: 5
+          command: COMPOSER_ROOT_VERSION=dev-master composer update --${{ matrix.stability }} --prefer-dist --no-interaction --no-progress
+
+      - name: Execute tests
+        run: vendor/bin/phpunit --verbose