Bug: Stop using show.partials.insert

### Description
https://github.com/projectblacklight/spotlight/blob/c7e6517421f7537168d12607b7fe5549dd48b588/spec/test_app_templates/catalog_controller.rb#L16

Blackight 9 no longer has `show.partials` as part of its configuration. 

### Steps to reproduce


### Expected behavior

