Unable to update from 23.04 to 23.10 ("Could not calculate the upgrade")

[Davide Macario]

Full error message:

```
Could not calculate the upgrade

An unresolvable problem occurred while calculating the upgrade.

This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.
```

The problem seems to be with PPAs, but I never added external repositories, plus I just upgraded from 22.04 to 23.04 with no issues.

ProblemType: Bug
DistroRelease: Ubuntu 23.04
Package: ubuntu-release-upgrader-core 1:23.04.7
ProcVersionSignature: Ubuntu 6.2.0-39.40-generic 6.2.16
Uname: Linux 6.2.0-39-generic x86_64
ApportVersion: 2.26.1-0ubuntu2.1
Architecture: amd64
CasperMD5CheckResult: pass
CrashDB: ubuntu
CrashReports:
 640:1000:124:1601858:2023-12-18 16:05:31.113037586 +0100:2023-12-18 16:05:32.113037586 +0100:/var/crash/_usr_libexec_tracker-extract-3.1000.crash
 640:127:124:4348900:2023-12-16 00:18:34.899098170 +0100:2023-12-16 00:18:34.903098158 +0100:/var/crash/_usr_bin_Xwayland.127.crash
CurrentDesktop: ubuntu:GNOME
Date: Mon Dec 18 19:15:56 2023
InstallationDate: Installed on 2023-05-09 (223 days ago)
InstallationMedia: Ubuntu 22.04.1 LTS "Jammy Jellyfish" - Release amd64 (20220809.1)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to lunar on 2023-12-18 (0 days ago)
VarLogDistupgradeAptHistorylog:
 Start-Date: 2023-12-18 19:15:09
 Requested-By: dmacario (1000)
 End-Date: 2023-12-18 19:15:09
VarLogDistupgradeApttermlog:
 Log started: 2023-12-18 19:15:09
 Log ended: 2023-12-18 19:15:09

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.