Stop running plugin-sanity job for doc and req changes

plugin-sanity job need not to be run for doc and req changes.
This commit adds irrelevant-files for this job.

Change-Id: I80cbd5c7cf97a626dee823cc18899b6388f438d6
diff --git a/.zuul.yaml b/.zuul.yaml
index ec6c59a..9432421 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -23,6 +23,13 @@
       tox_envlist: plugin-sanity-check
     voting: false
     timeout: 5000
+    irrelevant-files:
+      - ^.*\.rst$
+      - ^doc/.*$
+      - ^etc/.*$
+      - ^releasenotes/.*$
+      - ^tempest/hacking/.*$
+      - ^tempest/tests/.*$
     required-projects:
       - openstack/almanach
       - openstack/aodh