[docker-in-docker]: moby unavailable in Ubuntu 26.04

[sliekens]

Hi,

The mcr.microsoft.com/devcontainers/base:ubuntu base image was just updated to 26.04 and now there is a compatibility break with the docker-in-docker feature, which claims Moby is not supported in this release. (I don't know if that's actually true but I remember there was a similar problem with Debian 13 so it could be true.)

0.248 ===========================================================================
0.248 Feature       : Docker (Docker-in-Docker)
0.248 Description   : Create child containers *inside* a container, independent from the host's docker instance. Installs Docker extension in the container along with needed CLIs.
0.248 Id            : ghcr.io/devcontainers/features/docker-in-docker
0.248 Version       : 3.0.1
0.248 Documentation : https://github.com/devcontainers/features/tree/main/src/docker-in-docker
0.248 Options       :
0.248     VERSION="latest"
0.248     MOBY="true"
[2026-05-20T18:19:13.775Z] 
0.248     MOBYBUILDXVERSION="latest"
0.248     DOCKERDASHCOMPOSEVERSION="v2"
0.248     AZUREDNSAUTODETECTION="true"
0.248     DOCKERDEFAULTADDRESSPOOL=""
0.248     INSTALLDOCKERBUILDX="true"
0.248     INSTALLDOCKERCOMPOSESWITCH="false"
0.248     DISABLEIP6TABLES="false"
0.248 ===========================================================================
0.259 (!) The 'moby' option is not supported on ubuntu 'resolute' because 'moby-cli' and related system packages are not available in that distribution.
0.259 (!) To continue, either set the feature option '  "moby": false' or use a different base image.
0.259 ERROR: Feature "Docker (Docker-in-Docker)" (ghcr.io/devcontainers/features/docker-in-docker) failed to install! Look at the documentation at https://github.com/devcontainers/features/tree/main/src/docker-in-docker for help troubleshooting this error.
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