Add branch-network plugin to the checks pipeline

Change-Id: I3045162e96e3ea9383c1e6ac3269834d5da326f8

zuul.d/projects.yaml

diff --git a/zuul.d/projects.yaml b/zuul.d/projects.yaml
index 00a0515..a858582 100644
--- a/zuul.d/projects.yaml
+++ b/zuul.d/projects.yaml
@@ -99,6 +99,12 @@
         - gerrit-plugin-build
 
 - project:
+    name: plugins/branch-network
+    check:
+      jobs:
+        - gerrit-plugin-build
+
+- project:
     name: plugins/changemessage
     check:
       jobs: