[gardening] Mark vm/dart_2/regress_45898_test as Slow on dartkp-tsan-*
[gardening] Mark vm/dart_2/regress_45898_test as Slow on dartkp-tsan-*

TEST=ci
Fixes https://github.com/dart-lang/sdk/issues/47062

Change-Id: Ia0a33a10ddc00d80a90ee645325d52f43c3638cc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/212028
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>
Commit-Queue: Alexander Markov <239e774fd29abc1267878f57afe1a8a03e0ca887@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk