[gardening] Mark co19 LibTest/io/Stdin/readByteSync_A02_t01 flaky
[gardening] Mark co19 LibTest/io/Stdin/readByteSync_A02_t01 flaky

Issue https://github.com/dart-lang/co19/issues/175

TBR=kustermann@google.com

Change-Id: I1518f7a2a63d9347e858f67733202e07e932ae22
Reviewed-on: https://dart-review.googlesource.com/c/81361
Reviewed-by: Vyacheslav Egorov <72c81f38df725d8f1832acb9b5bb99563fc2f1b9@google.com>
Commit-Queue: Vyacheslav Egorov <72c81f38df725d8f1832acb9b5bb99563fc2f1b9@google.com>

dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk