pr-test: schedule 3x -> 2x; fix extra gate skipped on schedule

[hnyls2002]

Two related changes to the scheduled CI cadence.

1. Reduce schedule frequency from 3x/day to 2x/day

Last 30 scheduled runs of `pr-test.yml`:

Metric	Value
`cancelled`	9 / 30 (30%)
Required retry (`attempt > 1`)	10 / 30 (33%)
Median runtime	~6h
Current cadence	8h

Cadence (8h) is barely above runtime (~6h, often pushed past by GHA scheduling delay + GPU queue), so each new scheduled run lands while the previous one is still mid-execution. `concurrency.cancel-in-progress: true` then kills the prior run, wasting GPU runner time and forcing retries.

Between two adjacent 8h slots `main` typically accumulates only a handful of commits — three runs/day end up largely re-validating the same code while consuming a full fresh GPU runner suite each time.

PR push activity by hour (last ~1000 PR runs, UTC):

Hour	PR runs/h	Slot
01	82	current
09	65	current
17	20	current
11	20	new
23	28	new

New cron `0 11,23 * * *`:

• 12h cadence comfortably exceeds runtime → 0 overlap, 0 cancel-induced waste
• Both slots land in low PR-push hours → minimizes contention with developer pushes
• ~33% fewer scheduled GPU runner hours, plus elimination of retry/cancel waste

2. Fix: `pr-test-extra.yml` whole suite skipped on schedule path

Introduced by #25465: `call-gate` is intentionally skipped on `schedule` (no PR context for label check), but downstream test jobs gate on `needs.call-gate.result == 'success'`, treating `skipped` as failure and skipping the entire extra suite.

Example: https://github.com/sgl-project/sglang/actions/runs/26136273640

Fix: relax downstream `if` to `(success || skipped)` in all extra stage jobs and `sgl-kernel-build-wheels`. `!failure() && !cancelled()` still blocks the PR-path gate-failure case.

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CI States

Latest PR Test (Base): ❌ Run #26158094311
Latest PR Test (Extra): ❌ Run #26158094235

[gemini-code-assist]

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