#3463894 Temporary change to set default OPT_IN_TEST_NEXT_MAJOR to 1

This is step 1 of #3463894

includes/include.drupalci.main.yml

@@ -408,6 +408,8 @@ composer (next minor):
 
 composer (next major):
   extends: .composer-base
+  # @TODO Delete 'allow_failure:true' in MR242
+  allow_failure: true
   rules:
     - *opt-in-next-major-rule
     - when: always