From @dkwingsmt on an internal chat:

For some reason our engine CI no longer prints the actual error of the clang tidy check, but a bunch of useless logs, such as in
https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8752198650857229249/+/u/test:_test:_lint_host_debug/stdout?format=raw
Is it a known issue?

It is now! Definitely a regression, we need to fix this.