Tune prepare-providers-documentation skill classification and changelog rules

[vincbeck]

Improve the AI-driven provider documentation skill based on lessons learned from the last release wave (#69486).

Two issues observed during that run:

1. PRs that only touch build tooling or breeze templates — with the provider-scoped diff limited to regenerated files like README.rst or index.rst — were classified as misc instead of skip. Examples: Fix inconsistency between generated provider docs and pyproject.toml #68991 (fix provider docs vs pyproject.toml inconsistency) and Add explicit [tool.flit.sdist] sections to flit-based pyproject.tomls #65861 (add flit sdist sections). The deterministic classifier doesn't catch these because it only looks at file paths within the provider, not whether those files are template-generated output. Added explicit guidance in both the sub-agent prompt and the Phase 3 notes so the LLM correctly classifies these as skip.

2. Some PR titles use Conventional Commit prefixes (feat:, refactor:, etc.) which should not appear in changelogs. Added a rule in Phase 4b to strip these prefixes before writing changelog entries.

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

• Yes — Claude Code (Opus 4.6)

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• 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.

[eladkal]

just a thought.. we may want to ask the skill to notify RM if it detected top level block comment in the changelog that was not under scoped version.

[vincbeck]

just a thought.. we may want to ask the skill to notify RM if it detected top level block comment in the changelog that was not under scoped version.

Updated :)