Fixed registered field having wrong timezone

This happened with at least Postgres, which took it's server's timezone. It's complicated. Let's just set it from our side instead where we have some control.

spoolman/database/vendor.py

@@ -1,5 +1,6 @@
 """Helper functions for interacting with vendor database objects."""
 
+from datetime import datetime
 from typing import Optional
 
 from sqlalchemy import func, select
@@ -19,6 +20,7 @@ async def create(
     """Add a new vendor to the database."""
     db_item = models.Vendor(
         name=name,
+        registered=datetime.utcnow().replace(microsecond=0),
         comment=comment,
     )
     db.add(db_item)