Merge lane: jaah

Merge lane run: batch the queued PRs, run the full gate (if any) once on their merged tree, and merge the batch when it is green. Filed by the control plane (`app/merge_lane.py::ensure_lane`).

Merged #6308 (8f8bffa5d) and #6309 (ed0ace510). The merged tree passed the quick gate (5872 passed). Ejected nothing. Develop is green; the vale-red record was for an old sha, and Vale passes on ed0ace5. Batch took 46s, 28s of it the gate.