Remove instance variable @group multiple assignment

CHANGELOG

@@ -9,6 +9,7 @@ v 8.6.0 (unreleased)
   - Fix issue when pushing to projects ending in .wiki
   - Fix avatar stretching by providing a cropping feature (Johann Pardanaud)
   - Don't load all of GitLab in mail_room
+  - Memoize @group in Admin::GroupsController (Yatish Mehta)
   - Indicate how much an MR diverged from the target branch (Pierre de La Morinerie)
   - Strip leading and trailing spaces in URL validator (evuez)
   - Return empty array instead of 404 when commit has no statuses in commit status API

app/controllers/admin/groups_controller.rb

@@ -55,7 +55,7 @@ def destroy
   private
 
   def group
-    @group = Group.find_by(path: params[:id])
+    @group ||= Group.find_by(path: params[:id])
   end
 
   def group_params