When using dynamic schema, the schema file is not shown in the admin UI (Files tab) by default. It is hidden because (as per the section comment):
// Make sure that if the schema is managed, we don't allow editing.
But we don't have editing interface for those files (
SOLR-5287 was backed out), so the reason is not valid and makes reviewing schema just that bit harder.
The fix is probably just editing out that section, unless there are tests specifically for that.