Log message:
Mass-change BUILD_DEPENDS to TOOL_DEPENDS outside mk/.

Almost all uses, if not all of them, are wrong, according to the
semantics of BUILD_DEPENDS (packages built for target available for
use _by_ tools at build-time) and TOOL_DEPEPNDS (packages built for
host available for use _as_ tools at build-time).

No change to BUILD_DEPENDS as used correctly inside buildlink3.

As proposed on tech-pkg:
https://mail-index.netbsd.org/tech-pkg/2023/06/03/msg027632.html

Log message:
mailman3: add version 3.3.8

Mailman is free software for managing electronic mail discussion and
e-newsletter lists. Mailman is integrated with the web, making it easy
for users to manage their accounts and for list owners to administer
their lists. Mailman supports built-in archiving, automatic bounce
processing, content filtering, digest delivery, spam filters, and
more.