Nightly CI: run at 2:00 AM Pacific instead of evening

[aidangarske]

What

Change the Nightly CI cron from 0 2 * * * (02:00 UTC, roughly 7 PM Pacific) to 0 9 * * * (09:00 UTC = 2:00 AM Pacific / PDT).

Why

The previous 02:00 UTC schedule fires in the evening Pacific time, which overlaps with normal pushes to main during the workday. Because every workflow shares the concurrency group ${{ github.workflow }}-${{ github.ref }} with cancel-in-progress: true, and nightly.yml re-dispatches all workflows on ref: 'main', a delayed nightly run can collide with an in-flight push run and cancel it (recently seen on commit 6456084, where 30+ push jobs were cancelled mid-run).

Moving the schedule to 2:00 AM Pacific (overnight, 09:00 UTC) keeps the nightly run in a low-activity window and clear of working-hours pushes to main.

Note

This reduces the collision window but does not remove the root cause: nightly re-dispatching on ref: 'main' shares the push concurrency group. A follow-up could scope nightly's concurrency separately or drop the re-dispatch.

[Copilot]

Pull request overview

This PR updates the repository’s scheduled “Nightly CI” GitHub Actions workflow to run overnight in Pacific time, reducing the chance that nightly re-dispatch cancels in-flight push workflows on main due to shared concurrency settings.

Changes:

• Adjust the nightly.yml cron schedule from 0 2 * * * (02:00 UTC) to 0 9 * * * (09:00 UTC).
• Update the schedule comment to reflect the new intended run window.

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