[Satellite 6] upgrade fails on`foreman-rake db:migrate failed`

Issue

Running foreman-maintain upgrade run --target-version 6.4.z fails on error foreman-rake db:migrate failed!:

Execute db:migrate
== 20190205142619 AddContentConstraints: migrating ============================
-- change_column(:katello_product_contents, :content_id, :integer, {:null=>false})
   -> 0.0038s
-- change_column(:katello_product_contents, :product_id, :integer, {:null=>false})
   -> 0.0018s
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:
PG::ForeignKeyViolation: ERROR:  update or delete on table "katello_contents" violates foreign key constraint "katello_product_content_content_id_fk" on table "katello_product_contents" 
DETAIL:  Key (id)=(2403) is still referenced from table "katello_product_contents".
: DELETE FROM "katello_contents" WHERE "katello_contents"."id" = $1