Stop logging git repo rsync output

It's super chatty and not really what we need in life.

Change-Id: I6b45649ed316c49c0b49292fd5b81665e0f154ec
diff --git a/playbooks/roles/prepare-workspace/tasks/main.yaml b/playbooks/roles/prepare-workspace/tasks/main.yaml
index d8a5316..6a997fb 100644
--- a/playbooks/roles/prepare-workspace/tasks/main.yaml
+++ b/playbooks/roles/prepare-workspace/tasks/main.yaml
@@ -19,3 +19,4 @@
   synchronize:
     dest: "{{ prepare_workspace_root }}"
     src: "{{ zuul.executor.src_root }}"
+  no_log: true