tools/build/make.py: Add missing comma to fix tinderbox and worlds

The missing comma meant this was interpreted as a single target called
"tinderboxworlds", and so neither tinderbox nor worlds were recognised
as being MI targets (i.e. still required TARGET(_ARCH) to be given).

Fixes: 5157b451c654 ("tools/build/make.py: Grow the list of MI targets")