Improve async void guidance

Author: guardrex

aspnetcore/blazor/components/event-handling.md

@@ -40,6 +40,9 @@ For event handling:
 
 :::moniker-end
 
+> [!IMPORTANT]
+> The Blazor framework doesn't track `void`-returning asynchronous methods (`async`). As a result, the entire process fails when an exception isn't caught if `void` is returned. Always return a <xref:System.Threading.Tasks.Task>/<xref:System.Threading.Tasks.ValueTask> from asynchronous methods.
+
 The following code:
 
 * Calls the `UpdateHeading` method when the button is selected in the UI.

aspnetcore/blazor/components/index.md

@@ -638,7 +638,7 @@ Razor syntax for C# control structures, directives, and directive attributes are
 
 ### Asynchronous methods (`async`) don't support returning `void`
 
-The Blazor framework doesn't track `void`-returning asynchronous methods (`async`). As a result, exceptions aren't caught if `void` is returned. Always return a <xref:System.Threading.Tasks.Task> from asynchronous methods.
+The Blazor framework doesn't track `void`-returning asynchronous methods (`async`). As a result, the entire process fails when an exception isn't caught if `void` is returned. Always return a <xref:System.Threading.Tasks.Task>/<xref:System.Threading.Tasks.ValueTask> from asynchronous methods.
 
 ### Nested components