Change default BMO branch to main

This change is part of the changes aimed to remove offensive language
from the Nordix repositories.

Change-Id: I611725c5af7f92c817279068f23f64a134a4bc41
diff --git a/jjb/airship/job_ipa_image_building_test.yml b/jjb/airship/job_ipa_image_building_test.yml
index 10d8b52..c06fed1 100644
--- a/jjb/airship/job_ipa_image_building_test.yml
+++ b/jjb/airship/job_ipa_image_building_test.yml
@@ -63,7 +63,7 @@
         description: 'Bare Metal Operator repository commit hash to build'
     - string:
         name: BMO_BRANCH
-        default: 'master'
+        default: 'main'
         description: 'Bare Metal Operator repository branch to build'
     - string:
         name: IPA_BUILDER_BRANCH