🤖 tests: WorkflowService interrupt-join test saw two terminations in CI #7750

WorkflowService > interrupting a run with an active runner > a second interrupt during the drain joins the first failed once in CI: the runner was terminated twice (expect(terminations).toBe(1), received 2, WorkflowService.test.ts:747).

• Run: https://github.com/coder/xum/actions/runs/41015515127 (Unit 3/6, PR 🤖 refactor: split maybeStartQueuedTasksFromReservations, part 1: launch CAS, bookkeeping and plans #7745, which changes only taskService.ts; the test does not use TaskService).
• Locally it passed 20 of 20 runs (--rerun-each 20).

Either the test races, or a second interrupt that arrives at a narrow point does not join the first and terminates the runner again. The second case would be a real double termination. Check which one.

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