fix: fix clean performance fix

[bethesque]

@barthez I worked out what the issue was. The joins needed to be fully qualified, because the second join .left_outer_join(:verifications, pact_version_id: :id) inferred that the join was meant to link the verifications table with the pact publications table, when it should have been the pact_versions table.

# broken query
db[:pact_versions]
.left_outer_join(:pact_publications, pact_version_id: :id)
.left_outer_join(:verifications, pact_version_id: :id)
.select(Sequel[:pact_versions][:id])
.where(
  Sequel[:pact_publications][:id] => nil,
  Sequel[:verifications][:id] => nil
=> #<Sequel::SQLite::Dataset: "SELECT `pact_versions`.`id` FROM `pact_versions` 
LEFT OUTER JOIN `pact_publications` ON (`pact_publications`.`pact_version_id` = `pact_versions`.`id`) 

# This is where it goes wrong 
LEFT OUTER JOIN `verifications` ON (`verifications`.`pact_version_id` = `pact_publications`.`id`) 

WHERE ((`pact_publications`.`id` IS NULL) AND (`verifications`.`id` IS NULL))">


# working query
db[:pact_versions]
.left_join(:pact_publications, Sequel[:pact_publications][:pact_version_id]=> Sequel[:pact_versions][:id])
.left_join(:verifications, Sequel[:verifications][:pact_version_id]=> Sequel[:pact_versions][:id])
.select(Sequel[:pact_versions][:id])
.where(
  Sequel[:pact_publications][:id] => nil,
  Sequel[:verifications][:id] => nil
=> #<Sequel::SQLite::Dataset: "SELECT `pact_versions`.`id` FROM `pact_versions` 
LEFT JOIN `pact_publications` ON (`pact_publications`.`pact_version_id` = `pact_versions`.`id`) 
LEFT JOIN `verifications` ON (`verifications`.`pact_version_id` = `pact_versions`.`id`) 
WHERE ((`pact_publications`.`id` IS NULL) AND (`verifications`.`id` IS NULL))">

[barthez]

Oh! I see it now, thank you!