tools: travis_test.sh: Whitelist BART removal commit
Commits touching external/ subtrees are not allowed to be merged in master, so whitelist this subtree removal.
GitLab Maintenance scheduled for Thursday, 18th December 2025, from 7:00 AM to 10:00 AM BST. GitLab will be in read-only mode and experience short periods of complete downtime (up to 20 minutes) during this window.
Commits touching external/ subtrees are not allowed to be merged in master, so whitelist this subtree removal.