vacuumdb: Fix excluding multiple schemas with -N

vacuumdb: Fix excluding multiple schemas with -N

When specifying multiple schemas to exclude with -N parameters, none
of the schemas are actually excluded (a single -N worked as expected).
This fixes the catalog query to handle multiple exclusions and adds a
test for this case.

Backpatch to v16 where this was introduced.

Author: Nathan Bossart <[email protected]>
Author: Kuwamura Masaki <[email protected]>
Reported-by: Kuwamura Masaki <[email protected]>
Discussion: https://postgr.es/m/CAMyC8qp9mXPQd5D6s6CJxvmignsbTqGZwDDB6VYJOn1A8WG38w@mail.gmail.com
Backpatch-through: 16