Add python black formatting step to gdb buildbot

[Simon Marchi]

On 2022-07-17 18:10, Mark Wielaard wrote:
> Hi,
> 
> On irc Simon requested a python black formatting step for the gdb
> buildbot. And I saw Tom just fixed the last few formatting issues. So
> I added a "gdb black step" to the gdb-fedora-x86_64 builder (it seems
> fine to just run this on one builder instead on all - 19 now! - gdb
> builders).

Thanks for the quick delivery!

Simon