[TASK] Move the code style check to a decicated CI job

There is no need to run the code style check with every
PHP version.

.github/workflows/tests.yml

@@ -38,9 +38,39 @@ jobs:
         if: ${{ matrix.php > '8.1' }}
         run: composer install --prefer-dist --no-progress --no-suggest --optimize-autoloader --ignore-platform-req=php+
 
-      - name: Run cgl
-        if: ${{ matrix.php < '8.1' }}
-        run: composer cs
-
       - name: Run unit tests
         run: composer tests:unit
+
+  codestyle:
+    name: Code style
+    runs-on: ubuntu-22.04
+    strategy:
+      matrix:
+        php: ["8.1"]
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          extensions: zip
+          tools: composer:v2
+
+      - name: Get composer cache directory
+        id: composer-cache
+        run: echo "composer_cache_dir=$(composer config cache-files-dir)" >> $GITHUB_ENV
+
+      - name: Cache composer dependencies
+        uses: actions/cache@v3
+        with:
+          path: ${{ env.composer_cache_dir }}
+          key: ${{ runner.os }}-php-${{ matrix.php }}-composer-${{ hashFiles('**/composer.json') }}
+          restore-keys: ${{ runner.os }}-php-${{ matrix.php }}-composer-
+
+      - name: Install dependencies
+        run: composer install --prefer-dist --no-progress --no-suggest --optimize-autoloader
+
+      - name: Run cgl
+        run: composer cs