fixes CupertinoModalPopupRoute (#147823)

packages/flutter/lib/src/cupertino/route.dart

@@ -1096,7 +1096,7 @@ class CupertinoModalPopupRoute<T> extends PopupRoute<T> {
   @override
   Duration get transitionDuration => _kModalPopupTransitionDuration;
 
-  Animation<double>? _animation;
+  CurvedAnimation? _animation;
 
   late Tween<Offset> _offsetTween;
 
@@ -1142,6 +1142,12 @@ class CupertinoModalPopupRoute<T> extends PopupRoute<T> {
       ),
     );
   }
+
+  @override
+  void dispose() {
+    _animation?.dispose();
+    super.dispose();
+  }
 }
 
 /// Shows a modal iOS-style popup that slides up from the bottom of the screen.

packages/flutter/test/cupertino/route_test.dart

@@ -2666,6 +2666,36 @@ void main() {
 
     await tester.pump(const Duration(milliseconds: 400));
   });
+
+  testWidgets('CupertinoModalPopupRoute does not leak CurveAnimation',
+  // TODO(polina-c): remove when fixed https://github.com/flutter/flutter/issues/145600 [leak-tracking-opt-in]
+  experimentalLeakTesting: LeakTesting.settings.withTracked(classes: <String>['CurvedAnimation']),
+  (WidgetTester tester) async {
+    await tester.pumpWidget(MaterialApp(
+      home: Navigator(
+        onGenerateRoute: (RouteSettings settings) {
+          return PageRouteBuilder<dynamic>(
+            pageBuilder: (BuildContext context, Animation<double> _, Animation<double> __) {
+              return GestureDetector(
+                onTap: () async {
+                  await showCupertinoModalPopup<void>(
+                    context: context,
+                    semanticsDismissible: true,
+                    builder: (BuildContext context) => const SizedBox(),
+                  );
+                },
+                child: const Text('tap'),
+              );
+            },
+          );
+        },
+      ),
+    ));
+
+    // Push the route.
+    await tester.tap(find.text('tap'));
+    await tester.pumpAndSettle();
+  });
 }
 
 class MockNavigatorObserver extends NavigatorObserver {