Fix decreased prewarming pool due to inactivity timer.

When allocations fail and restart they are added again to the idle runners. The bug fixed with this commit is that the inactivity timer was not stopped at the restart. This led to the idle runner being removed when the timer expired.

internal/runner/nomad_manager.go

@@ -190,8 +190,11 @@ func (m *NomadRunnerManager) onAllocationStopped(runnerID string) (alreadyRemove
 		return false
 	}
 
-	_, stillActive := m.usedRunners.Get(runnerID)
-	m.usedRunners.Delete(runnerID)
+	r, stillActive := m.usedRunners.Get(runnerID)
+	if stillActive {
+		r.StopTimeout()
+		m.usedRunners.Delete(runnerID)
+	}
 
 	environment, ok := m.environments.Get(environmentID.ToString())
 	if ok {