Update playbook paths with extension

These playbook paths were missing ".yaml" extentions which fails when
implied matching goes away (Ie2519f2b4144761b8e4d17ec3299cf4238e16f08).

Change-Id: Iff04d894fffdcec0a0861d2460635b4c44a15ae4
diff --git a/tests/unit/test_v3.py b/tests/unit/test_v3.py
index 54cf111..b9c9b32 100755
--- a/tests/unit/test_v3.py
+++ b/tests/unit/test_v3.py
@@ -1935,8 +1935,8 @@
                 name: parent
                 roles:
                   - zuul: bare-role
-                pre-run: playbooks/parent-pre
-                post-run: playbooks/parent-post
+                pre-run: playbooks/parent-pre.yaml
+                post-run: playbooks/parent-post.yaml
 
             - job:
                 name: project-test