Address code review feedback - simplify to_exception call and clarify test comment

Co-authored-by: mykaul <4655593+mykaul@users.noreply.github.com>

Author: Copilot

cassandra/cluster.py

@@ -4789,10 +4789,7 @@ def _set_result(self, host, connection, pool, response):
                     log.warning("Host %s truncate error: %s.", host, response.summary)
                     if self._metrics is not None:
                         self._metrics.on_other_error()
-                    if hasattr(response, 'to_exception'):
-                        self._set_final_exception(response.to_exception())
-                    else:
-                        self._set_final_exception(response)
+                    self._set_final_exception(response.to_exception())
                     return
                 elif isinstance(response, PreparedQueryNotFound):
                     if self.prepared_statement:

tests/integration/simulacron/test_policies.py

@@ -443,7 +443,7 @@ def test_retry_policy_on_request_error(self):
 
             assert len(rf.attempted_hosts) == 1  # no retry
 
-        assert next(retry_policy.request_error) == 3
+        assert next(retry_policy.request_error) == 3  # 3 calls (excludes TruncateError)
 
         # Test TruncateError is not retried (no on_request_error call)
         clear_queries()