packages: Make set-base-dbg depend on set-optional-dbg

As set-base depends on set-optional, so should set-base-dbg depend on
set-optional-dbg. Otherwise, people who install set-base-dbg will be
missing a bunch of debug packages.

MFC after: 1 day
Reviewed by: emaste
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D53575