[Bugfix] Fix missing ARG in Dockerfile for arm64 platforms

[lkm-schulz]

The target vllm-openai-base uses the $TARGETPLATFORM variable to modify which version of bitsandbytes is installed based on the platform. However, the Dockerfile does not specify ARG TARGETPLATFORM for this target. When using Podman, the environment variable is thus not set and the build fails for linux/arm64 targets (e.g., GH200).

I believe Docker does not exhibit the same issue as ARG TARGETPLATFORM is declared for the base target.

[github-actions]

👋 Hi! Thank you for contributing to the vLLM project.

💬 Join our developer Slack at https://slack.vllm.ai to discuss your PR in #pr-reviews, coordinate on features in #feat- channels, or join special interest groups in #sig- channels.

Just a reminder: PRs would not trigger full CI run by default. Instead, it would only run fastcheck CI which starts running only a small and essential subset of CI tests to quickly catch errors. You can run other CI tests on top of those by going to your fastcheck build on Buildkite UI (linked in the PR checks section) and unblock them. If you do not have permission to unblock, ping simon-mo or khluu to add you in our Buildkite org.

Once the PR is approved and ready to go, your PR reviewer(s) can run CI to test the changes comprehensively before merging.

To run CI, PR reviewers can either: Add ready label to the PR or enable auto-merge.

🚀

[DarkLight1337]

Thanks for fixing!