Fix list import concurrently creating lists of the same name (#26372)

app/services/bulk_import_service.rb

@@ -162,10 +162,9 @@ def import_bookmarks!
 
   def import_lists!
     rows = @import.rows.to_a
+    included_lists = rows.map { |row| row.data['list_name'] }.uniq
 
     if @import.overwrite?
-      included_lists = rows.map { |row| row.data['list_name'] }.uniq
-
       @account.owned_lists.where.not(title: included_lists).destroy_all
 
       # As list membership changes do not retroactively change timeline
@@ -175,6 +174,10 @@ def import_lists!
       end
     end
 
+    included_lists.each do |title|
+      @account.owned_lists.find_or_create_by!(title: title)
+    end
+
     Import::RowWorker.push_bulk(rows) do |row|
       [row.id]
     end

spec/services/bulk_import_row_service_spec.rb

@@ -161,6 +161,12 @@
         end
 
         include_examples 'common behavior'
+
+        it 'does not create a new list' do
+          account.follow!(target_account)
+
+          expect { subject.call(import_row) }.to_not(change { List.where(title: 'my list').count })
+        end
       end
     end
   end