Support leoserver 'warning(s)' on startup: don't cancel auto-connect after only warnings.

[boltex]

As @edreamleo found out: Some installs of python 3.10 may give the following warning at the leoserver startup:

C:\Repos\leo-editor\leo\core\leoserver.py:1012: DeprecationWarning: There is no current event loop
asyncio.get_event_loop().create_task(self._asyncIdleLoop(delay / 1000, fn))

This will be fixed automatically in next python release, it also does not impede the server in any way.

On error pipe output, do not automatically cancel the startup : check for 'warnings' instead of 'errors' and continue with the normal startup.