api: ignore reference.php in .gitignore

This file changes too often.

Author: BacLuc

api/.gitignore

@@ -7,6 +7,7 @@
 /.env.local.php
 /.env.*.local
 /config/secrets/prod/prod.decrypt.private.php
+/config/reference.php
 /public/bundles/
 /var/
 /vendor/