[dart:io] Update httpparser size limit in CHANGELOG
[dart:io] Update httpparser size limit in CHANGELOG

Previous change has made a 8K size limit on http parser. It should be
put into CHANGELOG.md.

https://github.com/dart-lang/sdk/commit/36496047b4fc095013f29be351ae9021eb7cd832

Bug: https://github.com/flutter/flutter/issues/56580
Change-Id: I3e06848ff018ddacd022877b16ec69dc88f8a24a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/147322
Reviewed-by: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Commit-Queue: Zichang Guo <d26af3001798f91912fb1504666bca93c093d553@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