[Bug 2062042] Re: "No valid sources.list entry found" and "An upgrade might not succeed" when running "sudo do-dist-upgrade -d" on Ubuntu 23.10

[Nick Rosbrook]

Can you please attach the actual files so we can see the contents of the
sources?

** Changed in: ubuntu-release-upgrader (Ubuntu)
   Importance: Undecided => Medium

** Changed in: ubuntu-release-upgrader (Ubuntu)
       Status: New => Incomplete

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Title:
  "No valid sources.list entry found" and "An upgrade might not succeed"
  when running "sudo do-dist-upgrade -d" on Ubuntu 23.10

Status in ubuntu-release-upgrader package in Ubuntu:
  Incomplete

Bug description:
  I receive the message following message when performing a "sudo do-
  release-upgrade -d" on both my Ubuntu 23.10 system(s):

  Fetched 23.8 kB in 0s (0 B/s)                                                  
  Reading package lists... Done    
  Building dependency tree... Done 
  Reading state information... Done
  Fetched 0 B in 0s (0 B/s)                                                      

  Updating repository information

  No valid sources.list entry found

  While scanning your repository information no entry about mantic 
  could be found. 

  An upgrade might not succeed.

  Do you want to continue anyway?

  Continue [yN]

  The message "An upgrade might not succeed" is of concern, so obviously
  I can't proceed with the upgrade.

  My sources.list.d directory looks like this:

  cvpsmith at tars:/etc/apt/sources.list.d$ ls
  cubic-wizard-ubuntu-release-mantic.sources  slack.list
  google-chrome.sources                       spotify.sources
  jonaski-ubuntu-strawberry-lunar.sources     teams.list
  mozillateam-ubuntu-ppa-mantic.sources       ubuntu.sources
  nvhpc.list

  And here are the contents of "ubuntu.sources":

  Types: deb
  URIs: http://archive.ubuntu.com/ubuntu
  Suites: mantic mantic-updates mantic-security mantic-backports
  Components: main restricted universe multiverse
  Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg

  As is evident, removing "vscode.list" from sources.list.d/ has no
  effect.

  lsb_release -rd
  No LSB modules are available.
  Description:	Ubuntu 23.10
  Release:	23.10

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