Fix flaky cancelTasksWithIds integration test

Updated the `cancelTasksWithIds` test in `example/integration_test/general_test.dart` to use a larger file (`urlWithContentLength` instead of `workingUrl`) for the task being cancelled. This prevents the task from completing before the cancellation request is processed, resolving a race condition that caused the test to fail with `TaskStatus.complete` instead of `TaskStatus.canceled`.

Author: google-labs-jules[bot]

example/integration_test/general_test.dart

@@ -598,6 +598,9 @@ void main() {
       FileDownloader().registerCallbacks(
           taskStatusCallback: statusCallback,
           taskProgressCallback: progressCallback);
+      // download a large file, so we have time to cancel
+      task = DownloadTask(
+          url: urlWithContentLength, filename: defaultFilename);
       expect(await FileDownloader().enqueue(task), isTrue);
       var taskIds = await FileDownloader().allTaskIds();
       expect(taskIds.length, equals(1));