jobs: job tag no longer propogating to distsql flows

A few years ago, we [added ](https://github.com/cockroachdb/cockroach/pull/91630) some infra the job id tag's set in the job registry would be automatically propogated to distsql flows spun off by jobs. Yet, we[ observed](https://github.com/cockroachdb/cockroach/issues/143690#issuecomment-2809694356) a 25.1 schema change running an index backfill that did not have the job id propogated, so there's likely been a regression.

Fortunately, many jobs still manually tag their distsql flows with the job id tag. For example, [import ](https://github.com/msbutler/cockroach/blob/butler-pcr-priv-mixed/pkg/sql/importer/import_processor.go#L176)and [LDR](https://github.com/msbutler/cockroach/blob/butler-pcr-priv-mixed/pkg/crosscluster/logical/logical_replication_writer_processor.go#L275 ).

@rafiss fished up two PRs that could have affected things:
- https://github.com/cockroachdb/cockroach/pull/126972
- https://github.com/cockroachdb/cockroach/commit/f0c48f60f554e2ee20f2aea26ddbf459801fccf3

Jira issue: CRDB-50542

Epic CRDB-50858