Fix non-interactive Docker Hub authentication on ARM64 runner

[yeseorizi]

Summary

Fix the ARM64 self-hosted runner's Docker Hub authentication without invoking Docker Desktop's interactive macOS Keychain credential helper.

Problem

After PR #65 merged, the ARM64 workflow reached Docker Hub login but failed in the launchd runner with:

error saving credentials: error storing credentials - err: exit status 1,
out: User interaction is not allowed. (-25308)

Change

• create a job-scoped Docker config under $RUNNER_TEMP
• write the Docker Hub auth entry directly to that isolated config
• keep fork pull requests excluded from the self-hosted runner
• clear the temporary auth config in an always() cleanup step

The token remains a masked GitHub Actions secret and is not printed.

Validation

• pre-commit workflow/schema/yamllint checks: PASS
• workflow_dispatch on this branch: ARM64 run 34742095985 — PASS
• official image push: ioeslab/dave:ros2-arm-rdp
• published index digest: sha256:6a54823491647b16b6a7a10dc0defd7202b727e6aaaca7c6a6d998fccaf6caba
• manifest platform: linux/arm64

This PR only changes the ARM64 Docker workflow. It does not merge PRs #66–#68.