twisted: autopkgtest fails on test_flatten: "builtins.KeyError: 'root'"

Imported from Debian bug http://bugs.debian.org/1073996:

Message part #1
Source: twisted
Version: 24.3.0-1
Severity: serious
Tags: patch
Justification: 6a
X-Debbugs-Cc: <email address hidden>

Hello there,

Following some removal from Python itself, the following started to appear in autopkgtest:

2993s --- <exception caught here> ---
2993s File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1999, in _inlineCallbacks
2993s result = context.run(
2993s File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 519, in throwExceptionIntoGenerator
2993s return g.throw(self.value.with_traceback(self.tb))
2993s File "/usr/lib/python3/dist-packages/twisted/web/_flatten.py", line 435, in _flattenTree
2993s roots.append(frame.f_locals["root"])
2993s builtins.KeyError: 'root'

This is fixed upstream in https://github.com/twisted/twisted/pull/12213

I've cherry-picked the needed changes in a patch. I'll send a debdiff with everything shortly.

-- System Information:
Debian Release: trixie/sid
  APT prefers oracular
  APT policy: (500, 'oracular'), (400, 'oracular-proposed'), (200, 'noble-updates'), (200, 'noble'), (200, 'jammy-updates'), (200, 'jammy')
Architecture: amd64 (x86_64)

Kernel: Linux 6.8.0-31-generic (SMP w/12 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_WARN, TAINT_OOT_MODULE
Locale: LANG=fr_FR.UTF-8, LC_CTYPE=fr_FR.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled