Fix `Slider` semantic node size (#115285)

packages/flutter/test/widgets/semantics_debugger_test.dart

@@ -290,7 +290,7 @@ void main() {
   });
 
   testWidgets('SemanticsDebugger slider', (WidgetTester tester) async {
-    double value = 0.75;
+    double value = 0.50;
 
     await tester.pumpWidget(
       Directionality(
@@ -322,7 +322,7 @@ void main() {
     // interpreted as a gesture by the semantics debugger and sent to the widget
     // as a semantic action that always moves by 10% of the complete track.
     await tester.fling(find.byType(Slider), const Offset(-100.0, 0.0), 2000.0, warnIfMissed: false); // hitting the debugger
-    expect(value, equals(0.70));
+    expect(value, equals(0.45));
   });
 
   testWidgets('SemanticsDebugger checkbox', (WidgetTester tester) async {

packages/flutter_test/test/controller_test.dart

@@ -865,7 +865,7 @@ void main() {
         await tester.pumpWidget(const MaterialApp(home: _SemanticsTestWidget()));
 
         // We're expecting the traversal to start where the slider is.
-        final List<Matcher> expectedMatchers = <Matcher>[...fullTraversalMatchers]..removeRange(0, 8);
+        final List<Matcher> expectedMatchers = <Matcher>[...fullTraversalMatchers]..removeRange(0, 7);
 
         expect(
           tester.semantics.simulatedAccessibilityTraversal(start: find.byType(Slider)),
@@ -887,7 +887,7 @@ void main() {
         await tester.pumpWidget(const MaterialApp(home: _SemanticsTestWidget()));
 
         // We're expecting the traversal to end where the slider is, inclusive.
-        final Iterable<Matcher> expectedMatchers = <Matcher>[...fullTraversalMatchers].getRange(0, 9);
+        final Iterable<Matcher> expectedMatchers = <Matcher>[...fullTraversalMatchers].getRange(0, 8);
 
         expect(
           tester.semantics.simulatedAccessibilityTraversal(end: find.byType(Slider)),
@@ -909,7 +909,7 @@ void main() {
         await tester.pumpWidget(const MaterialApp(home: _SemanticsTestWidget()));
 
         // We're expecting the traversal to start at the text field and end at the slider.
-        final Iterable<Matcher> expectedMatchers = <Matcher>[...fullTraversalMatchers].getRange(1, 9);
+        final Iterable<Matcher> expectedMatchers = <Matcher>[...fullTraversalMatchers].getRange(1, 8);
 
         expect(
           tester.semantics.simulatedAccessibilityTraversal(