cherrypick #62758

[aslonnie]

declare ARG below FROM and explicitly re-set ENV from the ARG value, so the rayturbo build_arg takes effect in the RUN and /home/forge/.bazelrc is written with the correct cache URL.

[gemini-code-assist]

Code Review

This pull request modifies the manylinux-retag.Dockerfile by moving the BUILDKITE_BAZEL_CACHE_URL argument after the FROM instruction and adding it as an environment variable. Feedback suggests removing the ENV instruction because it unnecessarily persists potentially sensitive information in the image metadata and is redundant since the variable is already provided at runtime.

[gemini-code-assist]

Using ENV to store BUILDKITE_BAZEL_CACHE_URL is redundant and potentially insecure.

1. Security: ENV variables persist in the final image and are visible via docker inspect. If this URL contains sensitive information (e.g., credentials or tokens), it will be exposed in the image metadata.
2. Redundancy: The ARG instruction is sufficient to make the variable available to the RUN block during the build process. Additionally, ci/ray_ci/container.py already passes this variable at runtime via the --env flag, so setting it as a default ENV in the Dockerfile is unnecessary.

It is recommended to use only ARG for build-time configuration that doesn't need to persist in the image environment.

ARG BUILDKITE_BAZEL_CACHE_URL