network.switch_to_interface: catch 'task group terminated'

closes https://github.com/spesmilo/electrum/issues/7677
see https://github.com/spesmilo/electrum/issues/7677#issuecomment-1065170369

electrum/network.py

@@ -712,7 +712,14 @@ class Network(Logger, NetworkRetryManager[ServerAddr]):
             self.logger.info(f"switching to {server}")
             blockchain_updated = i.blockchain != self.blockchain()
             self.interface = i
-            await i.taskgroup.spawn(self._request_server_info(i))
+            try:
+                await i.taskgroup.spawn(self._request_server_info(i))
+            except RuntimeError as e:  # see #7677
+                if len(e.args) >= 1 and e.args[0] == 'task group terminated':
+                    self.logger.warning(f"tried to switch to {server} but interface.taskgroup is already dead.")
+                    self.interface = None
+                    return
+                raise
             util.trigger_callback('default_server_changed')
             self.default_server_changed_event.set()
             self.default_server_changed_event.clear()