Use `curly_braces_in_flow_control_structures ` for sample code (#104617)

* use `flutter_lints` for sample code

* update packages

* Revert "update packages"

This reverts commit 14da3c69a8da9a093ad9c2acd3fc5d6c7f7751ed.

* revert

examples/api/test/material/tooltip/tooltip.0_test.dart

@@ -17,8 +17,9 @@ void main() {
 
     TestGesture? gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     addTearDown(() async {
-      if (gesture != null)
+      if (gesture != null) {
         return gesture.removePointer();
+      }
     });
     await gesture.addPointer();
     await gesture.moveTo(const Offset(1.0, 1.0));

examples/api/test/material/tooltip/tooltip.1_test.dart

@@ -17,8 +17,9 @@ void main() {
 
     TestGesture? gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     addTearDown(() async {
-      if (gesture != null)
+      if (gesture != null) {
         return gesture.removePointer();
+      }
     });
     await gesture.addPointer();
     await gesture.moveTo(const Offset(1.0, 1.0));

examples/api/test/material/tooltip/tooltip.2_test.dart

@@ -17,8 +17,9 @@ void main() {
 
     TestGesture? gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
     addTearDown(() async {
-      if (gesture != null)
+      if (gesture != null) {
         return gesture.removePointer();
+      }
     });
     await gesture.addPointer();
     await gesture.moveTo(const Offset(1.0, 1.0));