设置显示我处于“开发分支”——我如何进入稳定版本？

我在四月份升级到了 24.04 开发分支。从那时起，我就一直保持系统更新。今天，在“设置”中，它显示我有“Ubuntu Noble Numbat（开发分支）”。

我该怎么做才能不进入“开发分支”？我的印象是，我只需要继续使用 apt 进行升级即可实现这一点。

我尝试过do-release-upgrade、、apt full-upgrade重启两次。没有发现任何变化。

更新

lsb_release -a：

No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu Noble Numbat (development branch)
Release:    24.04
Codename:   noble

这看起来不对。

输出apt update：

Hit:1 http://se.archive.ubuntu.com/ubuntu noble InRelease
Hit:2 https://dl.winehq.org/wine-builds/ubuntu noble InRelease       
Hit:3 http://security.ubuntu.com/ubuntu noble-security InRelease     
Get:4 http://ddebs.ubuntu.com noble InRelease [41.3 kB]              
Get:5 http://ddebs.ubuntu.com noble-updates InRelease [41.3 kB]
Fetched 82.7 kB in 1s (89.4 kB/s) 
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
N: Missing Signed-By in the sources.list(5) entry for 'http://ddebs.ubuntu.com'
N: Missing Signed-By in the sources.list(5) entry for 'http://ddebs.ubuntu.com'

缺少签名——是这个原因吗？

/etc/apt/sources.list 的内容：

# Ubuntu sources have moved to /etc/apt/sources.list.d/ubuntu.sources

/etc/apt/sources.list.d/ubuntu.sources 的内容：

Types: deb deb-src
URIs: http://se.archive.ubuntu.com/ubuntu/
Suites: noble
Components: main restricted universe multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg

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

新的来源格式看起来更容易阅读，但我不确定那里应该有什么。

更新 2

$ apt policy base-files
base-files:
  Installed: 13ubuntu9
  Candidate: 13ubuntu9
  Version table:
 *** 13ubuntu9 500
        500 http://se.archive.ubuntu.com/ubuntu noble/main amd64 Packages
        100 /var/lib/dpkg/status