Add irrelevant-files to nova-multiattach job in .zuul.yaml

This patch set adds irrelevant-files to nova-multiattach job
in .zuul.yaml because it is the only job without such a stanza
which is important for eliminating unnecessary Zuul resource
consumption, which, for example, is happening here:

https://review.openstack.org/#/c/583451/1

Change-Id: Ib48b735d65d2c005197edef9ab3011f93d0ad28c
diff --git a/.zuul.yaml b/.zuul.yaml
index fd3aa2a..4745ef5 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -277,7 +277,16 @@
               - ^playbooks/
               - ^roles/
               - ^.zuul.yaml$
-        - nova-multiattach
+        - nova-multiattach:
+            irrelevant-files:
+              - ^(test-|)requirements.txt$
+              - ^.*\.rst$
+              - ^doc/.*$
+              - ^etc/.*$
+              - ^releasenotes/.*$
+              - ^setup.cfg$
+              - ^tempest/hacking/.*$
+              - ^tempest/tests/.*$
         - tempest-full-parallel:
             irrelevant-files:
               - ^(test-|)requirements.txt$
@@ -373,7 +382,16 @@
               - ^tempest/tests/.*$
     gate:
       jobs:
-        - nova-multiattach
+        - nova-multiattach:
+            irrelevant-files:
+              - ^(test-|)requirements.txt$
+              - ^.*\.rst$
+              - ^doc/.*$
+              - ^etc/.*$
+              - ^releasenotes/.*$
+              - ^setup.cfg$
+              - ^tempest/hacking/.*$
+              - ^tempest/tests/.*$
         - tempest-scenario-all:
             irrelevant-files:
               - ^(test-|)requirements.txt$