Restore DagBag include_examples as a deprecated no-op argument

[patil-rushikesh]

Airflow 3.3.0 removed the include_examples argument from DagBag outright (#66161): the deprecation warning and the removal landed in the same PR, so users got no deprecation cycle across releases, and the removal was not mentioned in the release notes. This broke the common Dag-validation pattern DagBag(dag_folder=..., include_examples=False) with a TypeError on a minor-version upgrade.

This restores include_examples on DagBag.__init__ and DagBag.collect_dags as an accepted, deprecated argument: passing it emits RemovedInAirflow4Warning and is otherwise ignored, since example Dags are now provided exclusively through the per-provider bundles gated by [core] load_examples. (Honoring include_examples=True again would reintroduce the duplicate bundle registration that #66161 fixed; the no-op exactly matches old semantics for the dominant False usage.) The still-unreleased 66161.significant.rst newsfragment now documents the deprecation.

A backport to v3-3-test would unbreak 3.3.x users in 3.3.2.

closes: #70283

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

• Yes — Claude Code (Fable 5)

Generated-by: Claude Code (Fable 5) following the guidelines

[boring-cyborg]

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