fix(images): change zed branch name (#1225)

zed is unmaintained and the branch name changed from stable/zed to unmaintained/zed
diff --git a/images/neutron/Dockerfile b/images/neutron/Dockerfile
index 38b3d72..6d52763 100644
--- a/images/neutron/Dockerfile
+++ b/images/neutron/Dockerfile
@@ -18,7 +18,7 @@
 ARG NEUTRON_GIT_REF=ca25eb96f16dbe5ff1ca4446534f9a1d12fa7035
 ADD --keep-git-dir=true https://opendev.org/openstack/neutron.git#${NEUTRON_GIT_REF} /src/neutron
 RUN git -C /src/neutron fetch --unshallow
-ADD --keep-git-dir=true https://opendev.org/openstack/neutron-vpnaas.git#stable/zed /src/neutron-vpnaas
+ADD --keep-git-dir=true https://opendev.org/openstack/neutron-vpnaas.git#unmaintained/zed /src/neutron-vpnaas
 RUN git -C /src/neutron-vpnaas fetch --unshallow
 COPY patches/neutron /patches/neutron
 RUN git -C /src/neutron apply --verbose /patches/neutron/*