Add zuul plugin to check pipeline

Depends-On: https://gerrit-review.googlesource.com/c/zuul/ops/+/291561
Change-Id: Ic8e1e58f9ba6bc28de0a44fd91c4264ed7aafc6c

zuul.d/projects.yaml

diff --git a/zuul.d/projects.yaml b/zuul.d/projects.yaml
index a420710..279b18a 100644
--- a/zuul.d/projects.yaml
+++ b/zuul.d/projects.yaml
@@ -301,3 +301,9 @@
     check:
       jobs:
         - gerrit-plugin-build
+
+- project:
+    name: plugins/zuul
+    check:
+      jobs:
+        - gerrit-plugin-build