ci(fleet): pin next-wave aio-fleet workflows

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Summary

• Pins reusable workflow callers to aio-fleet main commit ce6221a.

What changed

• Updates build, upstream-check, release, and publish-release caller workflow refs.

Why

• Makes this repo use the landed next-wave reusable workflow implementation, including GitHub App token resolution and shared operator fixes.

Validation

• python -m aio_fleet sync-workflows --dry-run
• python -m aio_fleet validate --all
• trunk check --show-existing --all --no-fix --no-progress --color=false
• git diff --check