Improve epic swimlanes query performance for group board

Optmize query to load epics swimlanes on group
issue boards.

Changelog: performance
EE: true

ee/app/graphql/resolvers/board_groupings/epics_resolver.rb

@@ -36,6 +36,7 @@ module Resolvers
         list_service.execute.in_epics(accessible_epics).distinct_epic_ids
       end
 
+      # rubocop: disable CodeReuse/ActiveRecord
       def accessible_epics
         EpicsFinder.new(
           context[:current_user],
@@ -43,8 +44,9 @@ module Resolvers
           state: :opened,
           include_ancestor_groups: true,
           include_descendant_groups: board.group_board?
-        ).execute
+        ).execute.reorder(nil) # Not having order here increases performance, epics will be ordering on parent query anyway.
       end
+      # rubocop: enable CodeReuse/ActiveRecord
 
       def group
         board.project_board? ? board.project.group : board.group

ee/spec/graphql/resolvers/board_groupings/epics_resolvers_spec.rb

@@ -64,7 +64,7 @@ RSpec.describe Resolvers::BoardGroupings::EpicsResolver do
       it 'finds all epics for issues in the group board' do
         result = resolve_board_epics(group_board)
 
-        expect(result).to match_array([epic1, epic2, epic3])
+        expect(result).to eq([epic1, epic2, epic3])
       end
 
       it 'finds only epics for issues matching issue filters' do