Fix .NET 8 Installation for Debian 12 in Dev Container

[Abdullah Hashim (sombek)]

This PR updates the .NET 8 installation script in the python Dev Container to ensure compatibility with Debian 12 by adding an alternative installation method via dotnet-install.sh.

[Carlos Robles (croblesm)]

Thank you for this, and apologies for the long silence. You were right about the bug: the Python and Node templates installed the .NET SDK from a Debian feed that did not match the image, and on Arm64 there was no package at all, so the build failed outright.

The 2.0.0 refresh (#39) fixes it a different way, so I am closing this as superseded. `install-dotnet.sh` is gone; those templates now get the SDK from `ghcr.io/devcontainers/features/dotnet`, which resolves the right package for the distribution and the architecture. That also removed the mismatch class of bug entirely rather than correcting one instance of it.

CI now builds every template on `ubuntu-latest` and `ubuntu-24.04-arm` on each pull request, so this cannot regress unnoticed. Thanks for reporting it and for the fix.