DowntimeStore: be more paranoid about duplicate ts

Author: Thomas-Gelf

library/Eventtracker/Engine/Downtime/DowntimeStore.php

@@ -217,7 +217,9 @@ protected static function safeNow(?int $now): int
         if ($now === null) {
             $now = Time::unixMilli();
         }
-        if ($now === self::$lastNow) {
+        if ($now < self::$lastNow && self::$lastNow - $now < 300_000) {
+            $now = self::$lastNow + 1;
+        } elseif ($now === self::$lastNow) {
             $now += 1;
         }