Add missing word to code comment for clarity (#15443)

Author: bmac

packages/scheduler/src/Scheduler.js

@@ -343,8 +343,8 @@ function unstable_scheduleCallback(
   };
 
   // Insert the new callback into the list, ordered first by expiration, then
-  // by insertion. So the new callback is inserted any other callback with
-  // equal expiration.
+  // by insertion. So the new callback is inserted after any other callback
+  // with equal expiration.
   if (firstCallbackNode === null) {
     // This is the first callback in the list.
     firstCallbackNode = newNode.next = newNode.previous = newNode;