Update referenced FK to include partition_id for ci_stages

Problem

Each referenced FK must include the partitioning key in order to partition ci_stages.

Solution

Rewrite the following FKs to include partition_id.

Referenced by:
    TABLE "p_ci_builds" CONSTRAINT "fk_3a9eaa254d" FOREIGN KEY (stage_id) REFERENCES ci_stages(id) ON DELETE CASCADE

• https://docs.gitlab.com/ee/development/database/table_partitioning.html#step-4---enforce-foreign-key-constraint