Change ironic-image branch to main in ipa test

This change is related to the changes aimd to remove offensive
language from the Nordix repositories.

Change-Id: Ife9085f7f1d15e5b3699c9a7d174a326df5c4eb0
diff --git a/jjb/airship/job_ipa_image_building_test.yml b/jjb/airship/job_ipa_image_building_test.yml
index c06fed1..2c0efd9 100644
--- a/jjb/airship/job_ipa_image_building_test.yml
+++ b/jjb/airship/job_ipa_image_building_test.yml
@@ -43,7 +43,7 @@
         description: 'Ironic Image repository commit hash to build'
     - string:
         name: IRONIC_IMAGE_BRANCH
-        default: 'master'
+        default: 'main'
         description: 'Ironic image repository branch to build'
     - string:
         name: IRONIC_INSPECTOR_REFSPEC