packages: limit parallelism of dpkg-buildpackage

This MR limits the parallelism of dpkg-buildpackage during package building. This change likely addresses build stability issues or resource constraints that can occur when building Debian packages with excessive parallelism, ensuring more reliable package builds in the Tezos build system.

The change focuses on optimizing the package building process by controlling the concurrent operations during the dpkg-buildpackage phase.

scheduled pipeline: https://gitlab.com/tezos/tezos/-/pipelines/2036155776