Bug fix: update normalised_to, not just to after letter sanitise

When a precompiled letter is sent to us, we set the `to` field as
'Provided as PDF' in
1c1023a877/app/v2/notifications/post_notifications.py (L100-L104)

This then also sets `normalised_to` as `providedaspdf`.

However, when template preview sanitises the letter, pulls out the
address and gives it to the API, we were only setting `to` to be
the new address and had forgotten to also amend `normalised_to` to
be the normalised version. This meant that for all these letters
we accidentally left `normalised_to` as `providedaspdf`. The impact
of this was that we can not then search for these letters in the
admin user interface as they rely on the `normalised_to` field
containing the recipient address.

This commit fixes that bug by also setting the `normalised_to`
field

app/celery/letters_pdf_tasks.py

@@ -479,6 +479,7 @@ def update_letter_pdf_status(reference, status, billable_units, recipient_addres
         update_dict.update({'postage': postage, 'international': True})
     if recipient_address:
         update_dict['to'] = recipient_address
+        update_dict['normalised_to'] = ''.join(recipient_address.split()).lower()
     return dao_update_notifications_by_reference(
         references=[reference],
         update_dict=update_dict)[0]