closes https://github.com/spesmilo/electrum/issues/7677
```
E/n | network | taskgroup died.
Traceback (most recent call last):
File "/opt/electrum/electrum/network.py", line 1204, in main
[await group.spawn(job) for job in self._jobs]
File "/home/voegtlin/.local/lib/python3.8/site-packages/aiorpcx/curio.py", line 297, in __aexit__
await self.join()
File "/opt/electrum/electrum/util.py", line 1255, in join
task.result()
File "/opt/electrum/electrum/network.py", line 1277, in _maintain_sessions
await maintain_main_interface()
File "/opt/electrum/electrum/network.py", line 1268, in maintain_main_interface
await self._ensure_there_is_a_main_interface()
File "/opt/electrum/electrum/network.py", line 1245, in _ensure_there_is_a_main_interface
await self._switch_to_random_interface()
File "/opt/electrum/electrum/network.py", line 648, in _switch_to_random_interface
await self.switch_to_interface(random.choice(servers))
File "/opt/electrum/electrum/network.py", line 714, in switch_to_interface
await i.taskgroup.spawn(self._request_server_info(i))
File "/home/voegtlin/.local/lib/python3.8/site-packages/aiorpcx/curio.py", line 204, in spawn
self._add_task(task)
File "/home/voegtlin/.local/lib/python3.8/site-packages/aiorpcx/curio.py", line 150, in _add_task
raise RuntimeError('task group terminated')
RuntimeError: task group terminated
```
I believe the "suppress spurious cancellations" block was added as SilentTaskGroup raised
CancelledError instead of RuntimeError for this scenario.
d7af868ed8