[nnbd_migration] fix typo in instrumentation test
[nnbd_migration] fix typo in instrumentation test

Change-Id: I042d9ace734bb003898ab391922df56d6f5d562e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/133248
Reviewed-by: Paul Berry <72d414e3a99fb120308437779d51667bcc0984eb@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