test: resolve duplicate bug0021 numbering in 900_bugs 🔢

After #144 landed, master had two `bug0021_*` files —
`bug0021_chained_vectorized_tuple_arith.ndc` (from the original #140
work, in master longer) and `bug0021_combinations_lazy_source.ndc`
(just merged via #144). Renumber the combinations test to bug0022
since chained-vectorized got there first, and bump this branch's
incompat-Dynamic test to bug0023.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Author: timfennis