Rename sha256 to checksum on LFS transfer payload

lib/gitlab/geo/lfs_transfer.rb

@@ -11,7 +11,7 @@ module Gitlab
       private
 
       def lfs_request_data(lfs_object)
-        { sha256: lfs_object.oid }
+        { checksum: lfs_object.oid }
       end
     end
   end

lib/gitlab/geo/lfs_uploader.rb

@@ -5,7 +5,7 @@ module Gitlab
         lfs_object = LfsObject.find_by(id: object_db_id)
 
         return error unless lfs_object.present?
-        return error if message[:sha256] != lfs_object.oid
+        return error if message[:checksum] != lfs_object.oid
 
         unless lfs_object.file.present? && lfs_object.file.exists?
           return error('LFS object does not have a file')