[VLM] Add Qwen3-VL generation test

[Isotr0py]

Purpose

• Following PR for [Model] Support Qwen3-VL Model Series #24727, add Qwen3-VL generation tests.

Test Plan

pytest -s -v tests/models/multimodal/generation/test_common.py -k qwen3_vl

Test Result

Test should pass

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• 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
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• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[DarkLight1337]

Should we wait until model release before actually merging this?

[Isotr0py]

Should we wait until model release before actually merging this?

I'm fine to wait until model release and Transformers upgrade, because this test won't run on CI without them.

The goal of PR is just to provide a test for generation correctness validation, so that we can run correctness test for other Qwen3-VL related PRs locally to avoid regression. So whether merge this PR or not won't be a big deal IMO.