Loading a blendfile allocates one or more windows that need to be freed.
Freeing those windows also calls `BKE_workspace_instance_hook_free()` to
free workspaces. However, in the `BlendfileLoadingBaseTest` test there are
no workspaces allocated. This caused an assertion failure, which was worked
around by not asserting when Blender is running in background mode.
Reviewed by @Severin via pair programming
f63d65ae5a