PR #39518: [Misc] Update deprecation warning for --model flag

• Repository: vllm-project/vllm
• Author: z1ying
• State: open | merged: False
• Link: https://github.com/vllm-project/vllm/pull/39518

Description (problem / solution / changelog)

Purpose

Fixes #39506

Problem

The deprecation warning for the --model flag in vllm serve currently references removal in v0.13. Since vLLM is now at v0.19, this warning is outdated and misleading.

Solution

Update the warning message to refer to "a future version" instead of a specific outdated version, so it remains accurate for current and future users.

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<details> <summary> Essential Elements of an Effective PR Description Checklist </summary>

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

</details>

Changed files

• vllm/utils/argparse_utils.py (modified, +1/-1)