codecheck: reformat with black, version 20.8b1

The formatting of grml2usb that was done with black, version 18.9b0
triggers changes with black 20.8b1-3 as present in current
Debian/unstable:

| black --check grml2usb
| would reformat grml2usb
| Oh no! 💥 💔 💥
| 1 file would be reformatted.
| make[2]: *** [Makefile:44: codecheck] Error 1

Applying the change via modern black though doesn't lead to any
changes with black, version 18.9b0, so let's use this.

Gbp-Dch: Ignore