fix: update mtls_utils import in secret_client.py

Co-authored-by: Xuan Yang <xygoogle@google.com>
PiperOrigin-RevId: 937555547

Author: xuanyang15

src/google/adk/integrations/secret_manager/secret_client.py

@@ -26,7 +26,7 @@
 from google.oauth2 import service_account
 
 from ... import version
-from ...utils import mtls_utils
+from ...utils import _mtls_utils
 
 USER_AGENT = f"google-adk/{version.__version__}"
 
@@ -112,7 +112,7 @@ def __init__(
     client_options = None
     if location:
       client_options = {
-          "api_endpoint": mtls_utils.get_api_endpoint(
+          "api_endpoint": _mtls_utils.get_api_endpoint(
               location,
               _DEFAULT_REGIONAL_ENDPOINT_TEMPLATE,
               _DEFAULT_MTLS_REGIONAL_ENDPOINT_TEMPLATE,

tests/unittests/integrations/secret_manager/test_secret_client.py

@@ -124,7 +124,7 @@ def test_init_with_auth_token(self, mock_secret_manager_client):
       "google.adk.integrations.secret_manager.secret_client.default_service_credential"
   )
   @patch(
-      "google.adk.integrations.secret_manager.secret_client.mtls_utils.get_api_endpoint"
+      "google.adk.integrations.secret_manager.secret_client._mtls_utils.get_api_endpoint"
   )
   def test_init_with_location(
       self,