message: Add testdata path in testing/helper.py
  This is to cover the case where TINK_SRC_PATH/testdata is present and should be used as testdata in non-bazel runs.
diff: @@ -34,7 +34,9 @@ def tink_py_testdata_path() -> str:
  testdata_paths = []
  if 'TINK_SRC_PATH' in os.environ:
  testdata_paths += [
  - os.path.join(os.environ['TINK_SRC_PATH'], 'python/testdata')
  + os.path.join(os.environ['TINK_SRC_PATH'], 'python/testdata'),
  + # TODO(b/233570181): Refactor this function to avoid duplicating paths.
  + os.path.join(os.environ['TINK_SRC_PATH'], 'testdata')
  ]
  if 'TEST_SRCDIR' in os.environ:
  # Bazel enviroment
  