feat: add copybara-test-base job

Change-Id: I25faf808049828aa661f3fb66c7c8c620212b388
diff --git a/zuul.d/jobs.yaml b/zuul.d/jobs.yaml
index 33046a5..bdc5be1 100644
--- a/zuul.d/jobs.yaml
+++ b/zuul.d/jobs.yaml
@@ -46,3 +46,18 @@
     secrets:
       - name: copybara_secrets
         secret: copybara-secrets
+
+- job:
+    name: copybara-test-base
+    parent: base
+    description: |
+      Base job for test jobs which deal with Copybara.
+
+      It doesn't set up the git credentials for the Copybara bot since
+      it is meant for jobs which are run pre-review.
+
+      For instance, it can be used to validate Copybara config files.
+    nodeset:
+      nodes:
+        - name: copybara
+          label: copybara