fix: upgrade Go toolchain to 1.26.5 for GO-2026-4970-stdlib

[chainloop-platform]

Summary

Bumped the repository Go toolchain directive from 1.26.4 to 1.26.5 and updated the goreleaser builder images to the matching golang:1.26.5 pinned digest. This applies the minimum patch recommended for the vulnerable Go standard library release line.

Vulnerability Fixed

GO-2026-4970-stdlib (HIGH): on Unix systems, os.Root can improperly follow a final-component symlink outside the intended root when the path ends with /.

Changes Made

• Updated go.mod from go 1.26.4 to go 1.26.5 so local and CI builds use the fixed Go standard library release.
• Updated app/controlplane/Dockerfile.goreleaser, app/cli/Dockerfile.goreleaser, and app/artifact-cas/Dockerfile.goreleaser from golang:1.26.4@sha256:68cb6d68bed024785b69195b89af7ac7a444f27791435f98647edff595aa0479 to golang:1.26.5@sha256:079e59808d2d252516e27e3f3a9c003740dee7f75e55aa71528766d52bcfc16a to keep the release builders on the same fixed toolchain.

Verification

Ran syft dir:. -o cyclonedx-json=/tmp/chainloop-sbom-jVCFKl.json followed by grype sbom:/tmp/chainloop-sbom-jVCFKl.json --only-fixed -o json against the patched repo/. Classification: resolved. grype completed successfully and GO-2026-4970-stdlib was not present in the scan results.

Risk Assessment

View the risk assessment in Chainloop