Upgrade break SSH authentication with private key

This line https://github.com/YunoHost-Apps/nextcloud_ynh/blame/4c9942cc837a46d5f12e9514813b91a6d8a8da7d/scripts/upgrade#L315 give nextcloud ACL permissions so `/home/%u/.ssh/authorized_keys` is impacted.

SO we have next the error:
```
Authentication refused: bad ownership or modes for file /home/USER/.ssh/authorized_keys
```