Changes

repo-install-test: debian 10: osmo-gbproxy only

The debian 10 repository has been officially disabled:
https://osmocom.org/news/308

However we just re-enabled a subset of the packages, osmo-gbproxy +
dependencies, because currently they are relevant for a customer. Adjust
the repo-install-test to deal with this subset of packages for debian 10
to fix that it is currently failing.

I have verified that repo-install-test works with this change for debian
10, 11 and 12. It currently doesn't run for debian 13 yet (OS#6934).

Related: SYS#7859
Change-Id: Id8d8cda8e399719f06aeb1843eb8f5ab12a90e8f