jobs/gerrit: don't build osmo-epdg for debian:11

After switching to a newer gtplib, a newer OTP is required that isn't in
debian 11. Disable it, as Pau suggested.

Related: https://gerrit.osmocom.org/c/erlang/osmo-epdg/+/36052/3#message-d76c9c565d6feea88ef2e596fc5554ddd2e52cc1
Change-Id: I6a9147aef85612f3fb00920edea8c6706954b007

jobs/gerrit-verifications.yml

@@ -193,7 +193,7 @@
           repos_url: '{gerrit_url}/erlang/{repos}'
           gerrit_project: 'erlang/{repos}'
           cmd: '{docker_run} {docker_img_erlang} {timeout_cmd} /build/contrib/jenkins.sh'
-          pipeline_binpkgs: "debian:11 debian:12"
+          pipeline_binpkgs: "debian:12"
 
       - osmo-e1-hardware:
           a2_name: JOB_TYPE