address review feedback

Author: parthea

google/api_core/operations_v1/abstract_operations_client.py

@@ -293,14 +293,14 @@ def __init__(
             client_options = client_options_lib.ClientOptions()
 
         # Create SSL credentials for mutual TLS if needed.
-        use_client_cert = os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false")
-        if use_client_cert.lower() not in ("true", "false"):
+        use_client_cert = os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false").lower()
+        if use_client_cert not in ("true", "false"):
             raise ValueError(
                 "Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be either `true` or `false`"
             )
         client_cert_source_func = None
         is_mtls = False
-        if use_client_cert.lower() == "true":
+        if use_client_cert == "true":
             if client_options.client_cert_source:
                 is_mtls = True
                 client_cert_source_func = client_options.client_cert_source