devcontainer: bump Go image to 1.26

[shuan1026]

Ref #21364

Align the devcontainer with the main branch Go 1.26.

Note: Use mcr.microsoft.com/devcontainers/go:1.26-bookworm. The stable 1.26-bookworm tag has not been published on MCR yet; this PR is prepared in advance and will be ready to merge once the tag becomes available.

---

MCR devcontainers/go 1.26-related tags (queried on 2026-03-03)

Source: https://mcr.microsoft.com/v2/devcontainers/go/tags/list

Tag	Status
dev-1.26	Available
dev-1.26-bookworm	Available
dev-1.26-trixie	Available
1.26-bookworm	Not yet published

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: shuan1026
Once this PR has been reviewed and has the lgtm label, please assign ahrtr for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[k8s-ci-robot]

Hi @shuan1026. Thanks for your PR.

I'm waiting for a etcd-io member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Details

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.