Convert ci_refs.last_updated_by_pipeline_id to BIGINT

As discussed in !16951 (comment 296840626) we need to migrate ci_refs.last_updated_by_pipeline_id to bigint.

The following discussion from !16951 (merged) should be addressed:

• @dosuken123 started a discussion: (+3 comments)

        t.bigint :last_updated_by_pipeline_id