Hide board promotions for group boards

We need a separate promotion for these, and in any event, none of the existing
promotions apply to people who can see group boards, as group boards is
EEP-only.

ee/app/helpers/ee/boards_helper.rb

 module EE
   module BoardsHelper
-    def board_data
-      parent = @group || @project
+    def parent
+      @group || @project
+    end
 
+    def board_data
       data = {
         board_milestone_title: board&.milestone&.title,
         focus_mode_available: parent.feature_available?(:issue_board_focus_mode).to_s
@@ -49,8 +51,8 @@ module EE
 
     def board_sidebar_user_data
       super.merge(group_id: @group&.id,
-                  focus_mode_available: @project.feature_available?(:issue_board_focus_mode).to_s,
-                  show_promotion: (show_promotions? && (!@project.feature_available?(:multiple_issue_boards) || !@project.feature_available?(:issue_board_milestone) || !@project.feature_available?(:issue_board_focus_mode))).to_s)
+                  focus_mode_available: parent.feature_available?(:issue_board_focus_mode).to_s,
+                  show_promotion: (@project && show_promotions? && (!@project.feature_available?(:multiple_issue_boards) || !@project.feature_available?(:issue_board_milestone) || !@project.feature_available?(:issue_board_focus_mode))).to_s)
     end
   end
 end

ee/app/views/shared/promotions/_promote_issue_board.html.haml

+- return unless @project
+
 .board-promotion-state
   .svg-container.center
     = custom_icon('icon_issue_board')