avoids errors when parameters of Bot change
now all derived classes are always compatible

if the streams stdout or stderr are already closed (e.g. during
shutdown), ignore an error at flushing these streams

the job name 'build' does not fit here and is not unique
ubuntu 20.04 is old, try 22.04

In Python 3.7, the logging of the previous bot run can end up in the logging of the next run, resulting in line 0 being:
"Processed 1 messages since last logging." (written at shutdown of that bot)

prevents undefined variable errors in stop() if the logger is not yet
initialized

these are accesses in stop(), so if the initialization fails before e.g.
__message_counter["since"] was set, stop() will fail to
to prevent this, create the variable beforehand
same for the other variables

strip nullbytes from first line of bot log
truncate log_stream before initializing bot instance
ignore rare errors when the logs of the previous bot run appears in the logs of the current bot run