fix: fix lint errors

Signed-off-by: Radhika Agrawal <agrawalradhika@google.com>

Author: agrawalradhika-cell

google/api_core/operations_v1/abstract_operations_base_client.py

@@ -304,7 +304,9 @@ def __init__(
             use_client_cert = mtls.should_use_client_cert()
         else:
             # if unsupported, fallback to reading from env var
-            use_client_cert_str = os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false").lower()
+            use_client_cert_str = os.getenv(
+                "GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"
+            ).lower()
             if use_client_cert_str not in ("true", "false"):
                 raise ValueError(
                     "Environment variable `GOOGLE_API_USE_CLIENT_CERTIFICATE` must be"