docker-outside-of-docker failed to install -> rep ubuntu/20.04/prod focal InRelease is not signed

Trying to use the images:
- https://mcr.microsoft.com/en-us/product/devcontainers/dotnet/tags
- `6.0-focal` published June 24, 2024
- `dev-8.0` published June 24, 2024

The deployment errors out seemingly due to docker-outside-of-docker. Not sure if this is the cause or just a symptom of the failure.

> 5.546 W: GPG error: https://packages.microsoft.com/ubuntu/20.04/prod focal InRel
> ease: The following signatures couldn't be verified because the public key is no
> t available: NO_PUBKEY EB3E94ADBE1229CF
> 5.546 E: The repository 'https://packages.microsoft.com/ubuntu/20.04/prod focal
> InRelease' is not signed.
> 5.547 ERROR: Feature "Docker (docker-outside-of-docker)" (ghcr.io/devcontainers/
> features/docker-outside-of-docker) failed to install! Look at the documentation
> at https://github.com/devcontainers/features/tree/main/src/docker-outside-of-doc
> ker for help troubleshooting this error.

It looks like the docker outside of docker feature install.sh only imports the Microsoft signing keys if Moby is used:
https://github.com/devcontainers/features/blob/414d3450434b9072f01afe80cab226c60088224a/src/docker-outside-of-docker/install.sh#L215-L229

I do notice the Sample project I'm using doesn't provide a Moby property, which per docker outside of docker docs, moby should be true by default. Not sure why the key setup isn't working.
https://github.com/Azure-Samples/azure-sql-library-app-blazor/blob/0a1ba8c97744d887f209d95c7f932ddf0eb8b04c/.devcontainer/devcontainer.json#L59-L61
```json
"ghcr.io/devcontainers/features/docker-outside-of-docker:1": {
"version": "latest"
}
```

Read src/docker-outside-of-docker/install.sh around lines 215-229, focusing on when Microsoft signing keys are imported. Reproduce the installation with the listed .NET devcontainer images and the sample devcontainer.json at lines 59-61, then verify whether the default Moby behavior applies. Done means the feature installs without the missing-key or unsigned-repository error.

Scritto dal modello di indicizzazione a partire dal testo della issue.