[FIX] mrp: update MO quantity when there are more than one move per line

The production.move_raw_ids usually contains only one move per bom_line_id;
it might not always be the case, as ccbd6712 used move[0] to get a singleton.
The following calls to _get_document_iterate_key, _log_activity_get_documents,
also require move to be a singleton, so we use replace move by move[0].

opw 2042099

closes odoo/odoo#35206

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>