Gradle's metadata for a platform does not provide a way to define
exclusions in the same way that can be done in <dependencyManagement>
in a Mavne bom. This means that Gradle 6 users lose the exclusions
that are defined in the pom as Gradle 6 will use the metadata rather
than the pom.

Until such a time as Gradle's metadata supports the configuration of
such exclusions we can avoid the problem by disabling the metadata's
publication.

Fixes gh-21350