fix UnboundLocalError

Bug: https://github.com/flutter/flutter/issues/127543
Change-Id: Ib076b1791c72d6fccb0ea659379770dea9deb30b
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/45020
Reviewed-by: Keyong Han <keyonghan@google.com>
Commit-Queue: Christopher Fujino <fujino@google.com>

recipes/devicelab/devicelab_test_drone.py

diff --git a/recipes/devicelab/devicelab_test_drone.py b/recipes/devicelab/devicelab_test_drone.py
index 85eb98c..970542f 100644
--- a/recipes/devicelab/devicelab_test_drone.py
+++ b/recipes/devicelab/devicelab_test_drone.py
@@ -135,6 +135,7 @@
   api.retry.run_flutter_doctor()
   test_runner_command = ['dart', 'bin/test_runner.dart', 'test']
   test_runner_command.extend(runner_params)
+  test_status = ''
   try:
     test_status = api.test_utils.run_test(
         'run %s' % task_name,