fix(admin): prevent excessive polling in notifications (#12868)

Co-authored-by: Your Name <you@example.com>

packages/admin/dashboard/src/components/common/infinite-list/infinite-list.tsx

@@ -77,6 +77,7 @@ export const InfiniteList = <
       startObserver.current = new IntersectionObserver(
         (entries) => {
           if (entries[0].isIntersecting && hasPreviousPage) {
+            startObserver.current?.disconnect()
             fetchPreviousPage()
           }
         },
@@ -88,6 +89,7 @@ export const InfiniteList = <
       endObserver.current = new IntersectionObserver(
         (entries) => {
           if (entries[0].isIntersecting && hasNextPage) {
+            endObserver.current?.disconnect()
             fetchNextPage()
           }
         },
@@ -97,8 +99,12 @@ export const InfiniteList = <
       )
 
       // Register the new observers to observe the new first and last children
-      startObserver.current?.observe(parentRef.current!.firstChild as Element)
-      endObserver.current?.observe(parentRef.current!.lastChild as Element)
+      if (parentRef.current?.firstChild) {
+        startObserver.current?.observe(parentRef.current.firstChild as Element)
+      }
+      if (parentRef.current?.lastChild) {
+        endObserver.current?.observe(parentRef.current.lastChild as Element)
+      }
     }
 
     // Clear the old observers