https://ci.chromium.org/ui/p/flutter/builders/prod/Linux%20Production%20Engine%20Drone/550083/overview
The test flutter/tools/clang_tidy/test/header_filter_regex_test.dart ensures that engine repo subdirectories are covered by a regular expression. The test is failing because a directory that doesn't exist in the repo is being found in a directory listing, and that extra directory isn't covered by the regular expression.
Guessing this is due to another test not cleaning up after itself, but if that's not the case it could also be an infra caching issue? Initially routing to team-engine.