[th/update-black] update python black version

Newer versions format code slightly different. In particular, they nicely interpret a trailing comman in an argument list, to wrap the lines and put each argument on a separate line.

Also, on our developer machines, we wouldn't have such an ancient black version. It's kinda important that everybody uses the same black version.

In practice, it was so far always possible to modify the code so that older and recent black versions format it the same. But by updating to a newer version, we no longer need that.