curtin cannot handle Debian testing

[Andreas Florath]

curtin is not able to handle Debian testing:

    File "/curtin/curtin/commands/main.py", line 202, in main
       ret = args.func(args)
    File "/curtin/curtin/commands/curthooks.py", line 1884, in curthooks
       builtin_curthooks(cfg, target, state)
    File "/curtin/curtin/commands/curthooks.py", line 1725, in builtin_curthooks
       setup_kernel_img_conf(target)
    File "/curtin/curtin/commands/curthooks.py", line 333, in setup_kernel_img_conf
       if tuple(map(int, lsb_info['release'].split('.'))) >= (19, 10):
    ValueError: invalid literal for int() with base 10: 'testing'
    invalid literal for int() with base 10: 'testing'

# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description: Debian GNU/Linux bullseye/sid
Release: testing
Codename: bullseye