Require a base job

This makes base jobs required and allows for a per-tenant default.

Story: 2001110
Task: 4793
Change-Id: I26ffddad8358c156cfac749ce98af70f3447f671
diff --git a/tests/fixtures/layouts/requirements-github.yaml b/tests/fixtures/layouts/requirements-github.yaml
index 891a366..f2ecd16 100644
--- a/tests/fixtures/layouts/requirements-github.yaml
+++ b/tests/fixtures/layouts/requirements-github.yaml
@@ -184,23 +184,36 @@
         comment: true
 
 - job:
+    name: base
+    parent: null
+
+- job:
     name: project1-pipeline
+
 - job:
     name: project2-trigger
+
 - job:
     name: project3-reviewusername
+
 - job:
     name: project4-reviewreq
+
 - job:
     name: project5-reviewuserstate
+
 - job:
     name: project6-newerthan
+
 - job:
     name: project7-olderthan
+
 - job:
     name: project8-requireopen
+
 - job:
     name: project9-requirecurrent
+
 - job:
     name: project10-label