Exit with failure code if clang-tidy finds linter issues

[jmagman]

Exit clang_tidy script with nonzero exit code if linter issues are found. This will allow the recipe step to fail when linter issues are found.

$ dart flutter/tools/clang_tidy/bin/main.dart --compile-commands out/ios_debug/compile_commands.json --repo flutter --verbose --lint-all
...
Lint problems found.
$ echo $?
1

Fixes flutter/flutter#93357

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[flutter-dashboard]

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[jmagman]

Who would have thought, returning 1 from this future still exits the script with a 0 code.

https://stackoverflow.com/questions/26976550/why-main-return-value-does-not-set-exitcode-in-dart