Update collections.md (#10396)

Author: milwad-dev

collections.md

@@ -589,6 +589,10 @@ collect(['1'])->containsOneItem();
 collect(['1', '2'])->containsOneItem();
 
 // false
+
+collect([1, 2, 3])->containsOneItem(fn ($item) => $item === 2);
+
+// true
 ```
 
 <a name="method-containsstrict"></a>