Do not set up the Osmocom repository inside osmocom-bb-host-master, it is done in debian-bullseye-build. Without this patch, we actually installed the debian 9 version of libosmocore-dev in the debian 11 container.
This is part 1/2 of fixing TTCN3-centos-bts-test, which has been failing since OSMOCOM_REPO_MIRROR was changed in osmo-ci.git. Part 2 is in osmo-ci I8201f34a0f9747eea78c358a626cc3981d7407c4.
