Fix new static warnings with Dart 3.3 (#2173)

Author: nex3

lib/src/js/compile.dart

@@ -250,7 +250,7 @@ List<String>? _normalizeNonCanonicalSchemes(Object? schemes) =>
     };
 
 /// Implements the simplification algorithm for custom function return `Value`s.
-/// {@link https://github.com/sass/sass/blob/main/spec/types/calculation.md#simplifying-a-calculationvalue}
+/// See https://github.com/sass/sass/blob/main/spec/types/calculation.md#simplifying-a-calculationvalue
 Value _simplifyValue(Value value) => switch (value) {
       SassCalculation() => switch ((
           // Match against...

lib/src/util/box.dart

@@ -13,7 +13,7 @@ class Box<T> {
 
   Box._(this._inner);
 
-  bool operator ==(Object? other) => other is Box<T> && other._inner == _inner;
+  bool operator ==(Object other) => other is Box<T> && other._inner == _inner;
 
   int get hashCode => _inner.hashCode;
 }