fix(api-core): resolve lint warnings in client_utils and tests

Author: hebaalazzeh

packages/google-api-core/google/api_core/gapic_v1/client_utils.py

@@ -91,7 +91,7 @@ def should_use_mtls_endpoint(client_cert_available: bool) -> bool:
         return client_cert_available
     else:
         raise MutualTLSChannelError(
-            f"Environment variable `GOOGLE_API_USE_MTLS_ENDPOINT` must be `never`, `auto` or `always`"
+            "Environment variable `GOOGLE_API_USE_MTLS_ENDPOINT` must be `never`, `auto` or `always`"
         )
 
 
@@ -170,4 +170,3 @@ def get_universe_domain(
     if not universe_domain:
         raise ValueError("Universe Domain cannot be an empty string.")
     return universe_domain
-

packages/google-api-core/tests/unit/gapic/test_client_utils.py

@@ -18,7 +18,6 @@
 
 import pytest
 from google.auth.exceptions import MutualTLSChannelError
-from google.auth.transport import mtls
 
 from google.api_core.gapic_v1.client_utils import (
     get_api_endpoint,
@@ -243,6 +242,3 @@ def test__get_universe_domain():
     with pytest.raises(ValueError) as excinfo:
         get_universe_domain("", None, MockClient._DEFAULT_UNIVERSE)
     assert str(excinfo.value) == "Universe Domain cannot be an empty string."
-
-
-