jobs/ttcn: Run ttcn3-epdg-test only under debian12

Test EPDG_Tests.TC_mt_ipv4_echo_req fails when running under debian11
(node build2-deb11build-ansible), most probably due to some kernel bug
fixed later on.
Since anyway osmo-epdg requires OTP from debian12, it makes no sense to
attempt to support older kernel version from debian11, so simply avoid
picking debian11 to run the tests.

Change-Id: I247853cbefa0864f54bad5e5b6597556c46a51e3
diff --git a/jobs/ttcn3-testsuites.yml b/jobs/ttcn3-testsuites.yml
index b367c49..fbc0f04 100644
--- a/jobs/ttcn3-testsuites.yml
+++ b/jobs/ttcn3-testsuites.yml
@@ -136,6 +136,8 @@
           timer: H 07 * * *
       - ttcn3-epdg-test:
           timer: H 07 * * *
+          # osmo-epdg requires OTP and kernel >= debian12:
+          node: build4-deb12build-ansible
 
       # debian latest stable
       - nplab-m3ua-test-latest: