Update the large table list in AddColumnWithDefaultToLargeTable cop

- ci_builds -- 33 million rows, 55 GB
- merge_request_diff_files -- 5 million rows, 9 GB (and growing rapidly)
- merge_request_diffs -- 5 million rows, 190 GB

rubocop/cop/migration/add_column_with_default_to_large_table.rb

@@ -20,8 +20,11 @@ module RuboCop
           'necessary'.freeze
 
         LARGE_TABLES = %i[
+          ci_builds
           events
           issues
+          merge_request_diff_files
+          merge_request_diffs
           merge_requests
           namespaces
           notes