Add not about Laravel 11's ensure() collection method.

README.md

@@ -5,6 +5,11 @@
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+> [!NOTE]  
+> Laravel 11 added the `ensure()` collection method that verifies that all elements of
+> a collection are of a given type or list of types. However, this verification does not
+> prevent items of different types to be added at a later time.
+
 ## Installation
 
 The package can be installed with [Composer]: