Fixes <https://issues.guix.gnu.org/65510>.
Without this import, 'shepherd-service-type' is not mapped, leading to
an error about missing 'system' target.
* gnu/home/services/dict.scm,
gnu/home/services/syncthing.scm: Add #:use-module clause.
Reported-by: Morgan Smith <Morgan.J.Smith@outlook.com>