Revert unintentional change from dart2wasm testing

Author: simolus3

packages/sqlite_async/test/utils/web_test_utils.dart

@@ -19,7 +19,7 @@ class TestUtils extends AbstractTestUtils {
 
   Future<void> _init() async {
     final channel = spawnHybridUri('/test/server/worker_server.dart');
-    final port = (await channel.stream.first as num).toInt();
+    final port = await channel.stream.first as int;
     final sqliteWasmUri = 'http://localhost:$port/sqlite3.wasm';
     // Cross origin workers are not supported, but we can supply a Blob
     var sqliteUri = 'http://localhost:$port/db_worker.js';