Reinstate testing of changes to requirements.txt

Change I0c1328237d2109b1d1d5dcb40f331fff1ab10257 recently prevented
running kolla deployment CI jobs against changes to some files,
including requirements.txt. This change reinstates testing of changes to
requirements.txt, since this can have an effect on the operation of
kolla ansible.

Change-Id: I3d839de9aed60cddebea7d1140f618d3261cca2a

.zuul.yaml

@@ -74,7 +74,7 @@
     irrelevant-files:
       - ^.*\.rst$
       - ^doc/.*
-      - ^(test-|)requirements.txt$
+      - ^test-requirements.txt$
       - ^releasenotes/.*$
     vars:
       scenario: aio