add missing type parameter on methods (#22096)

diff --git a/packages/flutter_tools/test/commands/packages_test.dart b/packages/flutter_tools/test/commands/packages_test.dart
index 95c7f46..5f74b3a 100644
--- a/packages/flutter_tools/test/commands/packages_test.dart
+++ b/packages/flutter_tools/test/commands/packages_test.dart
@@ -159,7 +159,7 @@
         pubOutput,
         pluginRegistrants,
         pluginWitnesses,
-      ].expand((List<String> list) => list);
+      ].expand<String>((List<String> list) => list);
       for (String path in allFiles) {
         final File file = fs.file(fs.path.join(projectPath, path));
         if (file.existsSync())
@@ -285,7 +285,7 @@
       final Future<Null> simulateUserInput = Future<Null>(() {
         mockStdio.simulateStdin('y');
       });
-      await Future.wait(<Future<Null>>[runPackages, runPrompt, simulateUserInput]);
+      await Future.wait<Null>(<Future<Null>>[runPackages, runPrompt, simulateUserInput]);
       final List<String> commands = mockProcessManager.commands;
       expect(commands, hasLength(2));
       expect(commands[0], matches(r'dart-sdk[\\/]bin[\\/]pub'));