bluetooth/aioble/examples/temp_sensor.py: Properly notifies on update.

[konistehrad]

I think this should be merged. The timeout_ms=None call in particular keeps something deep in the internals from blocking service queries from the central, and without this the central doesn't get timely updates.

[aetelani]

Thanks for example update. I was doing this myself because the current example in master was not working.

[dpgeorge]

Thanks for the contribution. I can confirm that both fixes are needed:

• for the char write, so that subscribers are notified
• for the disconnected, so that the temp sensor remains connected until the central initiates a disconnect