Add main branch reference for project infra

Change-Id: I192dc0af35fc5daab33000e20c2dcd480c50bca7
diff --git a/jjb/airship/job_master_clean.yml b/jjb/airship/job_master_clean.yml
index 45bc826..99de2d0 100644
--- a/jjb/airship/job_master_clean.yml
+++ b/jjb/airship/job_master_clean.yml
@@ -67,7 +67,7 @@
           url: "{ci_github_repo}"
           credentials-id: "{ci_github_jenkins_credentials_id}"
           branches:
-            - '{branch|master}'
+            - '{branch|main}'
           name: 'origin'
           refspec: '+refs/heads/*:refs/remotes/origin/*'
           wipe-workspace: True