Iceberg BOM references unpublished Kafka Connect runtime artifact

### Apache Iceberg version

1.11.0 (latest release) and `main`

### Query engine

Kafka Connect

### Please describe the bug 🐞

The Iceberg BOM includes `org.apache.iceberg:iceberg-kafka-connect-runtime`, but
that Maven artifact is not published; its [1.11.0 POM](https://repo.maven.apache.org/maven2/org/apache/iceberg/iceberg-kafka-connect-runtime/1.11.0/iceberg-kafka-connect-runtime-1.11.0.pom)
returns 404.

The runtime project [disables Maven publishing](https://github.com/apache/iceberg/blob/main/kafka-connect/build.gradle#L237-L240)
because it produces ZIP distributions. The published `iceberg-kafka-connect`,
`iceberg-kafka-connect-events`, and `iceberg-kafka-connect-transforms` artifacts
should remain in the BOM.

The BOM should exclude `iceberg-kafka-connect-runtime` until that artifact is
published. Related: #14986.

Start by locating the Iceberg BOM definition and compare its Kafka Connect entries with kafka-connect/build.gradle around the publishing configuration at lines 237-240. Confirm that iceberg-kafka-connect-runtime is excluded while iceberg-kafka-connect, iceberg-kafka-connect-events, and iceberg-kafka-connect-transforms remain present. Done means the BOM no longer references the unpublished runtime artifact.

Written by the indexing model from the issue text.