chore: phpstan modify

In this commit, modifications have been made to the .gitlab-ci.yml file to allow running PHPUnit on
PHP 8.3 in our pipeline. A new job `modify-job` was added which runs phpstan script with following
instructions:

- Keeping other autoloaders with `QUIQQER_OTHER_AUTOLOADERS=KEEP`
- Disabling progress display with `--no-progress`
- Removing memory limit with `--memory-limit=-1`
- Enabling debug mode with `--debug`

.gitlab-ci.yml

@@ -14,4 +14,9 @@ phpunit-php8.2:
 # Remove the entire phpunit-php8.3 block, to allow PHPUnit to run on PHP 8.3 in your pipeline
 phpunit-php8.3:
   rules:
-    - when: never
\ No newline at end of file
+    - when: never
+
+modify-job:
+  phpstan:
+    script:
+      - QUIQQER_OTHER_AUTOLOADERS=KEEP ./tools/phpstan --no-progress --memory-limit=-1 --debug