Manually build the SQL so that it properly skips Rails.

app/models/ci/runner.rb

@@ -29,7 +29,8 @@ module Ci
     scope :specific_for, ->(project) do
       # TODO: That `to_sql` is needed to workaround a weird Rails bug.
       #       Without that, placeholders would miss one and couldn't match.
-      where(locked: false).where.not(id: project.runners.to_sql).specific
+      where(locked: false).
+        where.not("id IN (#{project.runners.select(:id).to_sql})").specific
     end
 
     validate :tag_constraints