Fixed a very small typo in code comments. (#91498)

packages/flutter/lib/src/widgets/sliver.dart

@@ -752,7 +752,7 @@ class SliverChildListDelegate extends SliverChildDelegate {
 ///
 /// * [KeepAlive], which marks whether its child widget should be kept alive.
 /// * [SliverChildBuilderDelegate] and [SliverChildListDelegate], slivers
-///    which make usr of the keep alive functionality through the
+///    which make use of the keep alive functionality through the
 ///    `addAutomaticKeepAlives` property.
 /// * [SliverGrid] and [SliverList], two sliver widgets that are commonly
 ///    wrapped with [KeepAlive] widgets to preserve their sliver child subtrees.