Minor fix to max_retries check (#1955)

Author: rayokota

src/confluent_kafka/schema_registry/schema_registry_client.py

@@ -218,7 +218,7 @@ def __init__(self, conf: dict):
         self.max_retries = 3
         max_retries = conf_copy.pop('max.retries', None)
         if max_retries is not None:
-            if not isinstance(timeout, (int, float)):
+            if not isinstance(max_retries, (int, float)):
                 raise TypeError("max.retries must be a number, not " + str(type(max_retries)))
             self.max_retries = max_retries