Prevent ThingUpdater from getting stuck due to reordering of TICK sig…

…nals.

Signed-off-by: Yufei Cai <yufei.cai@bosch.io>

thingsearch/service/src/main/java/org/eclipse/ditto/thingsearch/service/updater/actors/ThingUpdater.java

@@ -284,7 +284,7 @@ private void handleTransition(final State previousState, final State nextState)
                         backOff = backOff.calculateNextBackOff();
                         delay = backOff.getRestartDelay();
                     }
-                    startSingleTimer(Control.TICK.name(), Control.TICK, delay);
+                    startTimerWithFixedDelay(Control.TICK.name(), Control.TICK, delay);
                     unstashAll();
                 }
                 default -> cancelTimer(Control.TICK.name());