Replace upgrade-check build failure with scheduled upgrade PR workflow

[potiuk]

Move upgrade checks from basic-tests.yml (where they failed the build) to
scheduled workflows that create draft PRs with the changes:

• main: Mon/Wed/Fri at 06:00 UTC
• v3-2-test: Tue/Thu at 06:00 UTC

The workflows use breeze ci upgrade in non-interactive mode. When upgrades
are found, a draft PR is created (or an existing one is updated via force push
and converted back to draft). A Slack notification is sent to
#internal-airflow-ci-cd so a human can undraft, review and merge.

Changes:

• Remove upgrade-check job from basic-tests.yml
• Add reusable upgrade-check.yml workflow (workflow_call)
• Add scheduled-upgrade-check-main.yml (Mon/Wed/Fri cron)
• Add scheduled-upgrade-check-v3-2-test.yml (Tue/Thu cron)
• Enhance breeze ci upgrade: --draft flag, stable branch naming
  (ci-upgrade-{branch}), existing PR detection, removed -w flag
  for CI compatibility
• Update ci_commands_config.py with new --draft option

---

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

• Yes — Claude Code (Claude Opus 4.6)

Generated-by: Claude Code (Claude Opus 4.6) following the guidelines

[github-actions]

Backport failed to create: v3-2-test. View the failure log Run details

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.

In matter of doubt please ask in #release-management Slack channel.

Status	Branch	Result
❌	v3-2-test

You can attempt to backport this manually by running:

cherry_picker dd0ff5a v3-2-test

This should apply the commit to the v3-2-test branch and leave the commit in conflict state marking
the files that need manual conflict resolution.

After you have resolved the conflicts, you can continue the backport process by running:

cherry_picker --continue

If you don't have cherry-picker installed, see the installation guide.

[jscheffl]

Cool!

Mini follow-up we need to check, if change from tooling requires code adjustments (like Mypy upgrade last week) then the commit is failing in pre-commit checks. So probably we need to change that commits are automated skipping pre-merge checks... but can be a follow-up as well.

[jscheffl]

@potiuk I assume we need to backport as the v3-2-test execution for maintenance branch must also run on this codebase, correct? (and same yields for #64856 then)