Add PHP version matrix to checks workflow

Test against all supported PHP versions (7.4, 8.0, 8.1, 8.2, 8.3, 8.4) to ensure compatibility across the entire supported range.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: JanTvrdik

.github/workflows/checks.yml

@@ -10,6 +10,8 @@ jobs:
         runs-on: ubuntu-latest
         strategy:
             fail-fast: false
+            matrix:
+                php-version: ['7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
         steps:
             -
                 name: Checkout code
@@ -18,7 +20,7 @@ jobs:
                 name: Setup PHP
                 uses: shivammathur/setup-php@v2
                 with:
-                    php-version: 8.4
+                    php-version: ${{ matrix.php-version }}
             -
                 name: Install dependencies
                 run: composer install --no-progress --prefer-dist --no-interaction