Fix ini-values format

Follow-up to 15d5620

Author: swissspidy

.github/workflows/reusable-testing.yml

@@ -309,7 +309,7 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: '${{ matrix.php }}'
-          ini-values: ${{ matrix.php != 'nightly' && 'zend.assertions=1, error_reporting=-1, display_errors=On' }}
+          ini-values: ${{ matrix.php != 'nightly' && 'zend.assertions=1, error_reporting=-1, display_errors=On' || '' }}
           extensions: gd, imagick, mysql, zip
           coverage: none
           tools: composer