Add dataclasses-json floor to common.ai llamaindex extra

[FrankYang0529]

Why

• The automated CI environment upgrade (https://github.com/apache/airflow/actions/runs/29136631210/job/86502091735) bumped marshmallow 3.26.2 → 4.3.0, which broke the Non-DB providers tests.
• llama-index-core calls RefDocInfo.to_dict() at runtime, so every llama-index code path fails with AttributeError: 'RefDocInfo' object has no attribute 'to_dict'. (https://github.com/apache/airflow/actions/runs/29136631210/job/86503145941)
• llama-index-core depends on dataclasses-json without any version bound. (https://github.com/run-llama/llama_index/blob/67514f63410c6d4c2344e7ca14b3ea7214d0bb84/llama-index-core/pyproject.toml#L59)
• dataclasses-json 0.3.1–0.6.7 needs marshmallow<4.0.0. (https://github.com/lidatong/dataclasses-json/blob/79631c6ff0525f348bbddb92170d5bb22f511700/setup.py#L20, https://github.com/lidatong/dataclasses-json/blob/dc63902eeb5e1c5ce1ea4e078c50e0eb9bc1a541/pyproject.toml#L14) and 0.2.6-0.3.0 needs marshmallow==3.0.0rc6 (https://github.com/lidatong/dataclasses-json/blob/baa0fcc5e92a3711b0b88c0fa0a602fc884ce9cb/setup.py#L20).
• To keep marshmallow 4, the resolver fell back to dataclasses-json 0.2.5. The newest release without the <4. However, this version doesn't have the to_dict() API. (lidatong/dataclasses-json@8e37cc3)

How

• Add a dataclasses-json>=0.6.7 floor to the llamaindex.

---

Was generative AI tooling used to co-author this PR?

• Yes - Claude Code

---

• Read the Pull Request Guidelines for more information. Note: commit author/co-author name and email in commits become permanently public when merged.
• For fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
• When adding dependency, check compliance with the ASF 3rd Party License Policy.
• For significant user-facing changes create newsfragment: {pr_number}.significant.rst, in airflow-core/newsfragments. You can add this file in a follow-up commit after the PR is created so you know the PR number.