[Merge] ~callmepk/ubuntu-release-upgrader:ubuntu/master into ubuntu-release-upgrader:ubuntu/master

[Balint Reczey]

This bug is not specific to WSL. It can be observed on all Ubuntu installations when running the following command as a normal user:

$ update-motd --show-only
Welcome to Ubuntu 20.04 LTS (GNU/Linux 5.4.0-29-lowlatency x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

 * MicroK8s passes 9 million downloads. Thank you to all our contributors!

     https://microk8s.io/

15 updates can be installed immediately.
0 of these updates are security updates.
To see these additional updates run: apt list --upgradable

/usr/lib/ubuntu-release-upgrader/release-upgrade-motd: 31: cannot create /var/lib/ubuntu-release-upgrader/release-upgrade-available: Permission denied

Please fix it in a generic way.
-- 
https://code.launchpad.net/~callmepk/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/384183
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