This PR fixes the scheduled nightly CI run failing with `fatal: tag
'nightly-YYYY-MM-DD' already exists` when a manual `workflow_dispatch`
has already created today's nightly tag.
The scheduled path now uses the same `-revK` revision logic that the
manual re-release path already has: if `nightly-2026-03-24` exists, it
creates `nightly-2026-03-24-rev1` (and so on). The existing guard
against creating nightlies when HEAD has a non-nightly tag (e.g. a
release tag) is preserved.
🤖 Prepared with Claude Code
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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