[Scheduler] Remove incorrect mention of subtracting time from jitter

As we can see in the code https://github.com/symfony/symfony/blob/6.3/src/Symfony/Component/Scheduler/Trigger/JitterTrigger.php we can only add time

Author: Te4g

scheduler.rst

@@ -151,7 +151,7 @@ the frequency of the message. Symfony provides different types of triggers:
 
 :class:`Symfony\\Component\\Scheduler\\Trigger\\JitterTrigger`
     A trigger that adds a random jitter to a given trigger. The jitter is some
-    time that it's added/subtracted to the original triggering date/time. This
+    time that is added to the original triggering date/time. This
     allows to distribute the load of the scheduled tasks instead of running them
     all at the exact same time.