Update CHANGELOG.md
Update CHANGELOG.md

Clarify cast example for const expressions

Closes #38181
https://github.com/dart-lang/sdk/pull/38181

GitOrigin-RevId: 6b11ef6fa885659a4680c12d433a0b2aa7a228ac
Change-Id: If37be42bbeb2a6da0ec655de340e738bf6cc34da
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/115260
Reviewed-by: Leaf Petersen <9bef692239b5f624cec8e2cd5249ab1939a377aa@google.com>

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