fix: dev: Do not follow symlinks when chowning the NZD database

When `named` runs as root, the per-view NZD database file is chowned
to the user `named` drops to. The chown call followed symlinks, so a
symlink at the database path could redirect the ownership change to an
unrelated file. The chown now refuses non-regular files and never
follows symlinks.

Closes #5905

Merge branch '5905-nzd-env-close-symlink-chown' into 'main'

See merge request isc-projects/bind9!11907