GH Actions/test workflow: further improve base ini values

Follow up on 18

Depending on the PHP version, `E_ALL` may not actual include all errors, so let's use `-1` instead which always will.
Also, let's enable `zend.assertions` in the ini settings as those may be used in tests.

.github/workflows/test.yml

@@ -36,7 +36,7 @@ jobs:
         uses: shivammathur/setup-php@v2
         with:
           php-version: ${{ matrix.php }}
-          ini-values: error_reporting=E_ALL, display_errors=On
+          ini-values: zend.assertions=1, error_reporting=-1, display_errors=On
           coverage: none
           tools: cs2pr