Update of pop-default-settings can break third-party repositories

[Badintral]

Distribution (run cat /etc/os-release):

NAME="Pop!_OS" VERSION="21.10" ID=pop ID_LIKE="ubuntu debian" PRETTY_NAME="Pop!_OS 21.10" VERSION_ID="21.10" HOME_URL="https://pop.system76.com" SUPPORT_URL="https://support.system76.com" BUG_REPORT_URL="https://github.com/pop-os/pop/issues" PRIVACY_POLICY_URL="https://system76.com/privacy" VERSION_CODENAME=impish UBUNTU_CODENAME=impish LOGO=distributor-logo-pop-os

Related Application and/or Package Version (run apt policy $PACKAGE NAME):

pop-default-settings: Installed: 5.1.0~1647298500~21.10~c9eebd7 Candidate: 5.1.0~1647298500~21.10~c9eebd7 Version table: *** 5.1.0~1647298500~21.10~c9eebd7 1001 1001 http://apt.pop-os.org/release impish/main amd64 Packages 1001 http://apt.pop-os.org/release impish/main i386 Packages 100 /var/lib/dpkg/status

Issue/Bug Description: The update of pop-default-settings to version 5.1.0~1647298500~21.10~c9eebd7, changes the version of third-party repositories, like VirtualBox, from "hirsute" to "impish", even though the "impish" version does not exist. Subsequent runs of sudo apt update fail with the following error:

Err:11` https://download.virtualbox.org/virtualbox/debian impish Release 404 Not Found [IP: 104.121.236.27 443] Get:12 http://us.archive.ubuntu.com/ubuntu impish-updates InRelease [115 kB] Get:13 http://us.archive.ubuntu.com/ubuntu impish-backports InRelease [101 kB] Reading package lists... Done
E: The repository 'https://download.virtualbox.org/virtualbox/debian impish Release' does not have a Release file. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.

Steps to reproduce (if you know):

1. Update pop-default-settings to version 5.1.0~1647298500~21.10~c9eebd7
2. Observe change (in repoman, in /etc/apt/sources.list.d/download-virtualbox-org-virtualbox-debian.list) of repository version from "hirsute" to "impish"

Expected behavior: The update of distribution repositories should either check that the corresponding third-party repository versions exist, or not update them at all.

Other Notes: N/A