Debusine APT repositories don't support apt-cacher-ng (406 Not Acceptable)

Testing in a current sid container, apt is unable to access the Django 5.2 repository using HTTP, through apt-cacher-ng:

# cat /etc/apt/sources.list.d/django.sources 
Types: deb
URIs: http://deb.debusine.debian.net/debian/developers-lamby_django_test
Suites: sid-django-5.2
Components: main
Signed-By:
 -----BEGIN PGP PUBLIC KEY BLOCK-----
 .
 mDMEaPF29xYJKwYBBAHaRw8BAQdA4tqJqtk5cnHZznmF8yQqovH7rx2Z8rLG9EMX
 oXvHRge0O0FyY2hpdmUgc2lnbmluZyBrZXkgZm9yIGRlYmlhbi9kZXZlbG9wZXJz
 LWxhbWJ5X2RqYW5nb190ZXN0iJAEExYKADgWIQQSPYILvsq3Lz2CHPJMJe3ui994
 sQUCaPF29wIbAwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgAAKCRBMJe3ui994seVY
 AP0S/qT3ebuAxI9F2rz+x6OsKktpZghc34iWV0D9gFC0mwEAi3wkZuefF4RedOcy
 4yArZdL5VMDk5sLACi7p9IVVMwM=
 =xoIj
 -----END PGP PUBLIC KEY BLOCK-----
# apt update
Get:1 http://deb.debian.org/debian sid InRelease [176 kB]
Get:2 http://deb.debian.org/debian sid/main amd64 Packages [10.2 MB]
Get:3 http://deb.debian.org/debian sid/main Translation-en [7454 kB] 
Err:4 http://deb.debusine.debian.net/debian/developers-lamby_django_test sid-django-5.2 InRelease
  406  Not Acceptable [IP: 10.96.216.1 3142]
Error: Failed to fetch http://deb.debusine.debian.net/debian/developers-lamby_django_test/dists/sid-django-5.2/InRelease  406  Not Acceptable [IP: 10.96.216.1 3142]
Error: The repository 'http://deb.debusine.debian.net/debian/developers-lamby_django_test sid-django-5.2 InRelease' is not signed.

This can be reproduced with:

curl -v http://deb.debusine.debian.net/debian/developers-lamby_django_test/dists/sid-django-5.2/InRelease -H 'Accept: application/octet-stream'