Changes

debian-bullseye-*: apt-key is deprecated, use [signed-by] instead

The following warning message appears when running apt-key:

  apt-key is deprecated. Manage keyring files in trusted.gpg.d instead

The apt-key man page mentions that the "use of apt-key is deprecated,
except for the use of apt-key del in maintainer scripts to remove
existing keys from the main keyring".  What's more, "apt-key will last
be available in Debian 11 and Ubuntu 22.04".

Additionally, while the deprecation message says to "manage keyring
files in trusted.gpg.d instead", the Debian wiki states otherwise.
It's recommended to store the keys in /usr/share/keyrings instead,
and then use the 'signed-by' option to reference them.

https://salsa.debian.org/apt-team/apt/-/commit/ee284d5917d09649b68ff1632d44e892f290c52f

Change-Id: I1cae4f49e72f5e4f9d703cdb8f6d117e18e3567c

osmo-uecups-latest: new Dockerfile

osmo-uecups is available in the latest feed since recently.

Change-Id: I89c16dd0a71d2461981d978d2abf36f62bb9b339
Related: SYS#5602

ttcn3-pgw-test: allow using osmo-uecups from the latest feed

Change-Id: I4f92577f062e8a9be29af83026214636dff19d78