Fix PHP version used by testing workflow

The fix is to use the action `shivammathur/setup-php@v2` to setup the proper PHP version in the test runner, replacing `php-actions/composer` which only ensured using the desired PHP version while installing the project dependencies.

.github/workflows/linters.yml

@@ -19,13 +19,13 @@ jobs:
         uses: actions/checkout@v2
         with:
           fetch-depth: 0
-      - name: Composer install
-        uses: php-actions/composer@v5
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
         with:
-          command: install
-          args: --ignore-platform-reqs --no-scripts
-          version: 2
-          php_version: 8.0
+          php-version: 8.0
+          tools: composer:v2
+      - name: Composer install
+        run: composer install --ignore-platform-reqs --no-scripts
       - name: PHPStan
         run: ./vendor/bin/phpstan analyse
       - name: PHP Code Sniffer

.github/workflows/tests.yml

@@ -22,17 +22,18 @@ jobs:
           - php: 8.1
             coveralls: false
     steps:
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          tools: composer:v2
+          coverage: xdebug
       - name: Checkout
         uses: actions/checkout@v2
         with:
           fetch-depth: 0
       - name: Composer install
-        uses: php-actions/composer@v5
-        with:
-          command: install
-          args: --ignore-platform-reqs --no-scripts
-          version: 2
-          php_version: ${{ matrix.php }}
+        run: composer install --ignore-platform-reqs --no-scripts
       - name: Run tests
         env:
           XDEBUG_MODE: coverage