don't assign a group when creating non-group curated lists

same as updating a list but for if a user changes their mind about curation when initially creating a list.

bookwyrm/views/list.py

@@ -61,6 +61,10 @@ class Lists(View):
         if not form.is_valid():
             return redirect("lists")
         book_list = form.save()
+        # list should not have a group if it is not group curated
+        if not book_list.curation == "group":
+            book_list.group = None
+            book_list.save()
 
         return redirect(book_list.local_path)