search/hit: Fix double unref

When I originally wrote the code, I expected to create a new icon
every time that function was called. That expectation changed, but
the code wasn't fully updated.

Use g_value_set_object() instead of g_value_take_object().

src/search/gcal-search-hit.c

@@ -109,7 +109,7 @@ gcal_search_hit_get_property (GObject    *object,
       break;
 
     case PROP_PRIMARY_ICON:
-      g_value_take_object (value, gcal_search_hit_get_primary_icon (self));
+      g_value_set_object (value, gcal_search_hit_get_primary_icon (self));
       break;
 
     default: