Lower merge-queue check timeout from 360 to 120 min #1149

The merge-queue check timeout in ruleset 24668460 was raised from 90 to 360 minutes as a stopgap on 2026-10-08. The data supports lowering it to 120 minutes.

Numbers (CI workflow, merge_group event, 2026-10-01 to 2026-10-08, run start to last update):

• 45 successful runs: p50 47 min, p90 81 min, max 111 min. A 120-minute timeout would have evicted none of them.
• 17 failed and 10 cancelled in the same window.
• On 2026-10-08 a semantic conflict between Fix open bun issues (#992, #861, #784, #764, #735, #635, #599, #578, #497, #443, #371) #1009 and Make the vendored-to-hosted takeover atomic #1039 (rewrite() lost an argument) failed every entry built on Fix open bun issues (#992, #861, #784, #764, #735, #635, #599, #578, #497, #443, #371) #1009. That was 6 runs at 15:14 UTC (all four test/coverage jobs failed at about 2-4 min). The queue was then rebuilt twice: 1117 at 15:33, and 1110/1106/1103/1091 at about 15:55, cancelled at 16:29. Entries enqueued before 15:14 were still in a fresh batch at 16:37.

Why it matters: the check timeout only applies when a run hangs or never reports. At 360 min, a stuck ci-ok holds the queue head, and the up-to-5 entries built on it, for up to 6 hours before eviction. At 120 min it's 2 hours, and no healthy run in the last week came near that.

Related: #1146 makes a doomed merge-group run fail ci-ok early instead of waiting for the slowest e2e leg. #1133 shards the merge-group critical path (~46 min to ~20 min). Once both land, 90 min would again leave about 4x headroom over p50.

Recommended: check timeout 120 min now; 90 min after #1133 lands. Keep the build concurrency at 5.

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