The GPG key for Yarn has expired, again, it seems like this happened before:
#370

Example from mcr.microsoft.com/devcontainers/python:dev-3.14-bookworm running apt update
#18 0.335 Err:4 https://dl.yarnpkg.com/debian stable InRelease
#18 0.335 The following signatures were invalid: EXPKEYSIG 23E7166788B63E1E Yarn Packaging
#18 1.061 Reading package lists...
#18 1.500 W: GPG error: https://dl.yarnpkg.com/debian stable InRelease: The following signatures were invalid: EXPKEYSIG 23E7166788B63E1E Yarn Packaging

There is an issue in Yarnpkg about it, I guess this would need to be fixed before the images are recreated
yarnpkg/yarn#9216

If you remove yarn you can run apt-get. It seems using v1 or Yarn is not so advisable these days?
https://github.com/devcontainers/images/blob/main/src/python/manifest.json#L92-L95