Add member_namespace association to import/export

app/models/member.rb

@@ -28,7 +28,6 @@ class Member < ApplicationRecord
   belongs_to :user
   belongs_to :source, polymorphic: true # rubocop:disable Cop/PolymorphicAssociations
   belongs_to :member_namespace, inverse_of: :namespace_members, foreign_key: 'member_namespace_id', class_name: 'Namespace'
-  belongs_to :namespace, inverse_of: :namespace_route
   has_one :member_task
 
   delegate :name, :username, :email, :last_activity_on, to: :user, prefix: true

lib/gitlab/import_export/project/import_export.yml

@@ -904,6 +904,7 @@ excluded_attributes:
     - :release_id
   project_members:
     - :source_id
+    - :member_namespace_id
     - :invite_email_success
     - :state
   group_members:

spec/lib/gitlab/import_export/all_models.yml

@@ -136,6 +136,7 @@ project_members:
 - source
 - project
 - member_task
+- member_namespace
 merge_requests:
 - status_check_responses
 - subscriptions