Prek: Prefer gh auth over GitHub token env

[leeyspaul]

GH_TOKEN / GITHUB_TOKEN no longer shadow a valid gh auth login credential when prek helpers resolve a GitHub token.

This applies the same GitHub auth precedence used by Breeze to local prek scripts: explicit token arguments still win, then helpers try gh auth token with token env vars removed, then they fall back to ambient token env vars for CI/token-only environments.

Updated paths:

• upgrade_important_versions.py via retrieve_gh_token(...)
• download_k8s_schemas.py via optional token resolution, preserving unauthenticated fallback

Tests cover explicit-token precedence, cleaned gh auth token precedence, env fallback, missing gh, blank gh auth token output, and the existing fatal help path when a required token cannot be resolved.

I kept these as small scripts/ci/prek helpers instead of importing the Breeze helper because the two paths run in different package/runtime contexts.

Breeze owns airflow_breeze.utils.github, while these are Airflow-owned local prek scripts that can run as standalone hook/script entries. Making prek helpers importairflow_breeze would couple local hook execution to Breeze being importable in that environment. The logic is intentionally duplicated here, but kept minimal: token resolution only, not the broader Breeze gh command wrapper.

Breeze PR: #66255

Related: #55567

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

• Yes - GPT-5.5

Generated-by: GPT-5.5 following the guidelines

[boring-cyborg]

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[github-actions]

Backport successfully created: v3-2-test

Note: As of Merging PRs targeted for Airflow 3.X
the committer who merges the PR is responsible for backporting the PRs that are bug fixes (generally speaking) to the maintenance branches.

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Status	Branch	Result
✅	v3-2-test