[FIX] survey: allow to modify a completed survey

Updating a completed survey will raise an error with a traceback.

To reproduce the error:
(Use demo data)
1. Survey > Participations
2. Select a completed form
3. Change one answer, Save

Error: A traceback appears "[...] ValueError: Computing score requires a
question in arguments."

Here is an extract from the method concerned:
```python
@api.model
def _get_answer_score_values(self, vals, compute_speed_score=True):
    """
        [...]
    """
    user_input_id = vals.get('user_input_id')
    answer_type = vals.get('answer_type')
    question_id = vals.get('question_id')
    if not question_id:
        raise ValueError(_('Computing score requires a question in
arguments.'))
```
This method needs some information to work properly.

OPW-2488974

closes odoo/odoo#69842

Signed-off-by: Adrien Widart <adwid@users.noreply.github.com>