Add changelog and code refactor

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.9.0 (unreleased)
+  - Fix issue todo not remove when leave project !4150 (Long Nguyen)
   - Allow forking projects with restricted visibility level
   - Improve note validation to prevent errors when creating invalid note via API
   - Redesign navigation for project pages

app/models/members/project_member.rb

@@ -14,7 +14,7 @@ class ProjectMember < Member
   scope :in_projects, ->(projects) { where(source_id: projects.pluck(:id)) }
   scope :with_user, ->(user) { where(user_id: user.id) }
 
-  before_destroy { user.todos.where(project_id: source_id).each(&:destroy) if user }
+  before_destroy :delete_member_todos
 
   class << self
 
@@ -103,6 +103,10 @@ class ProjectMember < Member
 
   private
 
+  def delete_member_todos
+    user.todos.where(project_id: source_id).destroy_all if user
+  end
+
   def send_invite
     notification_service.invite_project_member(self, @raw_invite_token)