Fix: VT preferences

When checking the preferences for VTs set by the user, it used the value
provided by the script itself instead the one provided by the user (except
for type checkbox), so many values were not set to an empty string.

rust/src/openvas/pref_handler.rs

@@ -113,7 +113,7 @@ where
                         let value_aux: String = if class == *"checkbox" {
                             bool_to_str(&pref.value)
                         } else {
-                            value
+                            pref.value.to_string()
                         };
 
                         pref_list.insert(