[Data][CI] Move test_push_based_shuffle to postmerg

[win5923]

Description

As title.

Context:

• Push-based shuffle isn't used by default, and we haven't touched the code in years.
• Ray Data has premerge (must pass before you can land a PR) and postmerge CI. To make it easier to ship, we can move unimportant tests to postmerge.

Related issues

Closes #60417

Additional information

Optional: Add implementation details, API changes, usage examples, screenshots, etc.

[gemini-code-assist]

Code Review

This pull request moves the test_push_based_shuffle test to a post-merge CI job, likely to improve pre-merge CI speed. The changes correctly tag the test in the Bazel file and update the CI configuration to run it in new post-merge jobs. My review includes a suggestion to refactor the new CI jobs to improve maintainability by reducing code duplication.

[gemini-code-assist]

These two new post-merge test steps are nearly identical. To improve maintainability and reduce code duplication, you can combine them into a single matrix step. This is consistent with how other tests are configured in this file.

- label: ":database: data: postmerge arrow {{matrix.arrow_version}} tests"
  matrix:
    setup:
      arrow_version:
        - "v9"
        - "v23"
    adjustments:
      - with:
          arrow_version: "v9"
        build_name: "data9build-py3.10"
        depends_on: "data9build-multipy"
      - with:
          arrow_version: "v23"
        build_name: "datalbuild-py3.10"
        depends_on: "datalbuild-multipy"
  tags:
    - data
    - skip-on-premerge
  instance_type: medium
  commands:
    - >
      bazel run //ci/ray_ci:test_in_docker -- //python/ray/data/... //python/ray/air/... data
      --build-name {{matrix.build_name}} --python-version 3.10
      --only-tags skip-on-premerge
  depends_on: "{{matrix.depends_on}}"

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