Restore AMD scheduled canary, split README badges, fix Slack-state collision

[potiuk]

Summary

PR #66348 split the combined ci-amd-arm.yml into per-platform wrappers and intentionally deferred re-adding a schedule trigger to ci-amd.yml ("No schedule for now; ARM keeps the canary slot. Add a schedule: block here if/when AMD should also act as a scheduled canary"). Three things fell out of that:

1. The "Tests (AMD)" badge on the README pointed at a workflow that hadn't run on main since 2025-10-25 (it now only runs on PRs and release-branch pushes), so the badge was perpetually stale.
2. The notify-slack job at the bottom of ci-amd.yml is gated on github.event_name == 'schedule' and was therefore dead code: there was no schedule trigger left to fire it.
3. main on AMD had no scheduled CI monitor at all (ci-notification.yml only watches v3-2-test × ci-amd.yml, and the comment there assumes ARM is reported by its own notify-slack).

Changes

• ci-amd.yml — restore the previous AMD canary cron at minute :58 of the same hours ARM uses, so the two scheduled runs don't compete for runners at exactly the same minute.
• README.md — split the main build-status row into two badges (AMD + ARM), drop the obsolete 2.x row (still using the legacy ci.yml), keep 3.x AMD-only (ARM has no v3-2-test schedule). Click-throughs now go to the workflow page rather than the catch-all /actions URL.
• ci-amd.yml, ci-arm.yml, ci-image-checks.yml — disambiguate the slack-state artifact names. Before this PR the latent collision did not bite (AMD's notify-slack never fired); restoring the AMD schedule activates it. Each platform now writes its own slack-state-{tests,inventory}-<branch>-{amd,arm} artifact so the de-dup tracker in scripts/ci/slack_notification_state.py keeps independent state per platform.
• scripts/ci/prek/check_ci_workflows_in_sync.py — allow the new AMD-only schedule block and the per-platform artifact-name suffix as documented divergences.
• generated/PYPI_README.md — regenerated automatically by the generate-pypi-readme prek hook to mirror README.md.

related: #66348

Test plan

• Confirm both badges render in the README preview after merge
• Confirm ci-amd.yml fires on schedule (next slot at 01:58 / 07:58 / 13:58 / 19:58 UTC) and that the notify-slack job runs
• Confirm Slack messages for AMD and ARM use independent state artifacts (no spurious "still not fixed" or "all passing" cross-talk after the first scheduled cycle of each)

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

• Yes — Claude Code (Opus 4.7)

Generated-by: Claude Code (Opus 4.7) 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 022e35d 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.