ci: remove Docker Hub bootstrap from TKE checkin

[aptend]

Summary

• skip QEMU for native-only linux/amd64 image builds
• use the pinned IDC BuildKit mirror for both TKE checkin image paths
• keep multi-architecture callers on the existing QEMU behavior

Recent checkin runs failed before the MatrixOne build because setup-qemu/setup-buildx pulled tonistiigi/binfmt and moby/buildkit from Docker Hub, where the Shanghai DIND runner hit EOF and TLS handshake timeouts.

Validation

• actionlint .github/workflows/merge-trigger-tke.yaml
• resolved both the pinned manifest-list and amd64 manifest from the IDC registry
• bootstrapped a docker-container Buildx builder from the pinned IDC digest
• completed a linux/amd64 smoke build using the TCR Ubuntu base image
• git diff --check