CI: make libnetconf2-cpp available via Zuul

...so that a subsequent build of dependencies won't fail.

Change-Id: I0c4eb7df589add0be6ea655a49f792369126c72a
diff --git a/.zuul.yaml b/.zuul.yaml
index fb85f6b..bdede81 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -17,6 +17,7 @@
       - CzechLight/rousette
       - CzechLight/libyang-cpp
       - CzechLight/sysrepo-cpp
+      - CzechLight/libnetconf2-cpp
       - github/CESNET/libyang
       - github/sysrepo/sysrepo
       - github/CESNET/libnetconf2