[Trivial] Remove wrong format_message() conversion

This is a bug, follow up with the nova-cyborg-interaction patch,
comment by sean-k-mooney [1].

[1]https://review.opendev.org/#/c/631244/69/nova/compute/manager.py@2599

Closes-Bug: #1890428

Change-Id: I40bd9c0fa62c8087fa06af44b0b28dfe050fa1e6

Author: 1049965823

nova/compute/manager.py

@@ -2593,7 +2593,7 @@ def _build_resources(self, context, instance, requested_networks,
                 arqs = self._get_bound_arq_resources(
                     context, instance, accel_uuids)
             except (Exception, eventlet.timeout.Timeout) as exc:
-                LOG.exception(exc.format_message())
+                LOG.exception(exc)
                 self._build_resources_cleanup(instance, network_info)
                 compute_utils.delete_arqs_if_needed(context, instance)
                 msg = _('Failure getting accelerator requests.')