Fix "spec/migrations/swap_columns_for_system_note_metadata_id_spec.rb"

What does this MR do and why?

Fixes the migration spec failing in the CI gitlab-org/quality/engineering-productivity/master-broken-incidents#5091 (closed).

select true assigns a different column name depending on the environment. Locally the column name observed is bool while in the CI it can be seen as ?column? leading the rspec to fail as the test seeks to match for { 'bool' => true }.