Add PHP 8.3 to GitHub Workflows

Author: Valentin Wotschel

.github/workflows/php-tests.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         operating-system: [ ubuntu-latest ]
-        php-version: [ '8.0', '8.1', '8.2' ]
+        php-version: [ '8.0', '8.1', '8.2', '8.3' ]
 
     name: PHP ${{ matrix.php-version }} test on ${{ matrix.operating-system }}
 
@@ -46,10 +46,11 @@ jobs:
 
       - name: PHPUnit Tests
         run: |
-          if [[ ${{ matrix.php-version }} == '8.0' ]]; then
+          if [[ '${{ matrix.php-version }}' == '8.0' ]]; then
             vendor/bin/phpunit --configuration phpunit-9.6.xml --coverage-clover tests/coverage.xml
           else
             vendor/bin/phpunit --coverage-clover tests/coverage.xml
+          fi
 
       - name: Upload coverage reports to Codecov
         uses: codecov/codecov-action@v3