Fix typo in `list.length=` method comment
Fix typo in `list.length=` method comment

Change-Id: I35457f926446c9b77c34d7b2a967b6d9076ba055
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/169841
Auto-Submit: Karl Klose <49bc0b76cffb0b10cd8c84f9cabc97a31ffe6343@google.com>
Commit-Queue: Karl Klose <49bc0b76cffb0b10cd8c84f9cabc97a31ffe6343@google.com>
Commit-Queue: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Reviewed-by: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@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