Add checks plugin to check pipeline

This adds the checks plugin to the check pipeline.  Alternatively,
this change could be made in the checks repo itself in the .zuul.yaml
file. But we rather prefer to have all plugin pipelines in one single
place.

Change-Id: I18b9b39761703d8d0726c5a4d9e3365d60a8a7d8

zuul.d/projects.yaml

diff --git a/zuul.d/projects.yaml b/zuul.d/projects.yaml
index f22fce4..ae2f434 100644
--- a/zuul.d/projects.yaml
+++ b/zuul.d/projects.yaml
@@ -75,6 +75,12 @@
 # Other plugins:
 
 - project:
+    name: plugins/checks
+    check:
+      jobs:
+        - gerrit-plugin-build
+
+- project:
     name: plugins/code-owners
     check:
       jobs: