fix build

Author: parthea

tests/transport/test__custom_tls_signer.py

@@ -18,6 +18,7 @@
 import mock
 import pytest  # type: ignore
 from requests.packages.urllib3.util.ssl_ import create_urllib3_context  # type: ignore
+
 urllib3_pyopenssl = pytest.importorskip(
     "urllib3.contrib.pyopenssl",
     reason="urllib3.contrib.pyopenssl not available in this environment",
@@ -26,7 +27,7 @@
 from google.auth import exceptions
 from google.auth.transport import _custom_tls_signer
 
-urllib3.contrib.pyopenssl.inject_into_urllib3()
+urllib3_pyopenssl.inject_into_urllib3()
 
 FAKE_ENTERPRISE_CERT_FILE_PATH = "/path/to/enterprise/cert/file"
 ENTERPRISE_CERT_FILE = os.path.join(