Bump versions of buildbot to v3.11.7 and switch to Debian 12

[ynezz]

buildworker,buildmaster: bump Debian to version 12

Debian 11 LTS support ends in June 2026, so it's probably around the
time when support for the OpenWrt 24.10 release might end. Therefore,
let's switch to Debian 12, which should have LTS support until June 2028
and is the latest and greatest.

Bump buildbot to v3.11.7 release

Changes since current v3.11.1 release:

Bug Fixes

• Fixed GitPoller when repourl has the port specified (:issue:7822).
• Fixed ChoiceStringParameter fields with multiple would not store the selected values.
• Fixed unnecessary trimming of spaces in logs shown in the web UI (:issue:7774).
• Fixed favicon colors on build views in the web UI.
• Fixed the icon on the about page in the web UI.
• Fixed a regression where builds in waterfall view were no longer linking to the build page.
• Transfer build steps (:bb:step:FileUpload, :bb:step:DirectoryUpload, :bb:step:MultipleFileUpload, :bb:step:FileDownload, and :bb:step:StringDownload) now correctly remove the destination on failure, preventing partial content (:issue:2860).
• Fixed ReactUI when Buildbot is hosted behind a reverse proxy not at the URL's root (:issue:7260, :issue:7746).
• Fixed results color shown on the builder's header in the waterfall view.
• Fixed cases where the waterfall view could be squashed to a pixel high.
• Fixed several occasional data update glitches in the web frontend.
• Fixed the display of newly added builds in the Workers view in the web frontend.
• Fixed a regression where GitPoller would no longer register new changes (regression introduced in 3.11.3 in #7554).
• Fixed a bug that caused GitPoller running with git configured with the fetch.prune=true parameter to fail.
• Fixed a bug that caused GitPoller to miss changes when Buildbot is reconfigured.
• Reduced the length of directory names produced by GitPoller internally to avoid potential breakage on filesystems with low path and name length limits.
• Removed credentials from repourl used in the tracker branch name.
• Fixed an error in HgPoller when repository initialization fails (:issue:7488).
• Updated the Makefile to handle Windows paths and Python.
• Fixed the steps raw log download button.
• Fixed a regression in the React UI that prevented hosting Buildbot at a custom URL prefix, allowing support for multiple Buildbot instances on a single server.

Changes

• Buildbot will now raise an error when configured with multiple services of the same type and name (:issue:6987).
• Improved the flexibility of the scaling_waterfall setting to support floating-point values for a more condensed view.
• Added a web configuration setting to select whether build completion or start times are displayed.
• Added a revision info column in the web frontend.

Features

• Added MessageFormatterFunctionRaw, allowing complete customization of emitted messages. This feature has been available since 3.11.0 but was only recently announced.

Deprecations and Removals

• The pollinterval argument of various change sources has been deprecated with a warning in favor of pollInterval.

Improved Documentation

• Documented that ChangeSource does not support secrets (or any other renderables) and provided best practices for handling secret values in changes. Up until Buildbot 3.7, ChangeSource accidentally supported renderable arguments, which was undocumented behavior.