workflows: Remove xtask_support branch from CI trigger

xtask_support is used for testing the CI trigger.

Signed-off-by: Steven Lee <steven_lee@aspeedtech.com>

Author: stevenlee7189

.github/workflows/build-test.yml

@@ -9,7 +9,6 @@ on:
   pull_request:
     branches:
       - main
-      - xtask_support
 
 jobs:
   precommit: