title: Categories is not showing in custom post type
body: <p>I have registered a custom post type as follows:</p>
  <pre><code>//Register Custom Post Type Services
  register_post_type('services', array(
      'labels'              =&gt; array(
          'name'                =&gt; _x( 'Services', 'Post Type General Name', 'fk' ),
          'singular_name'       =&gt; _x( 'Service', 'Post Type Singular Name', 'fk' ),
          'menu_name'           =&gt; __( 'Services', 'fk' ),
          'parent_item_colon'   =&gt; __( 'Parent Service', 'fk' ),
          'all_items'           =&gt; __( 'All Services', 'fk' ),
          'view_item'           =&gt; __( 'View Service', 'fk' ),
          'add_new_item'        =&gt; __( 'Add New Service', 'fk' ),
          'add_new'             =&gt; __( 'Add New', 'fk' ),
          'edit_item'           =&gt; __( 'Edit Service', 'fk' ),
          'update_item'         =&gt; __( 'Update Service', 'fk' ),
          'search_items'        =&gt; __( 'Search Service', 'fk' ),
          'not_found'           =&gt; __( 'Not Found', 'fk' ),
          'not_found_in_trash'  =&gt; __( 'Not found in Trash', 'fk' ),
          'new_item'           =&gt; __( 'New Service' ),
      ),
  
  
      'supports'            =&gt; array( 'title', 'editor', 'excerpt', 'author', 'thumbnail', 'revisions', 'custom-fields' ),
      // You can associate this CPT with a taxonomy or custom taxonomy.
      'taxonomies'          =&gt; array( 'categories' ),
      'hierarchical'        =&gt; false,
      'public'              =&gt; true,
      'show_ui'             =&gt; true,
      'show_in_menu'        =&gt; true,
      'show_in_nav_menus'   =&gt; true,
      'show_in_admin_bar'   =&gt; true,
      'menu_position'       =&gt; 20,
      'can_export'          =&gt; true,
      'has_archive'         =&gt; false,
      'exclude_from_search' =&gt; false,
      'publicly_queryable'  =&gt; true,
      'capability_type'     =&gt; 'post',
      'show_in_rest'        =&gt; true,
      'menu_icon'           =&gt; 'dashicons-megaphone',
      'query_var'           =&gt; true,
      'rewrite'             =&gt; array( 'slug' =&gt; 'services' ),
  
  ));
  </code></pre>
  <p>Here, I have just used categories as the taxonomy, but it is not showing the options to select categories while trying to create one of the services.</p>
  <p>I don't need any custom categories, just regular categories options would be fine. By the way, before the line for <code>taxonomy</code> was commented and I added that later only.</p>