role alert has an implicit aria-live value of assertive (#863)

Elements with the role alert have an implicit aria-live value of assertive, and an implicit aria-atomic value of true.

https://www.w3.org/TR/wai-aria-1.2/#alert

And I added a <button type="button"> as <button> is a submit and can cause form submissions when it is a descendant of <form> elements

Author: BogdanCerovac

guides/accessibility/accessibility/guide.md

@@ -332,9 +332,9 @@ Live regions let assistive tech announce content updates that aren't tied to nav
 
 ```html
 <!-- Session Timeout Warning with controls -->
-<div role="alert" aria-live="assertive" class="timeout-warning">
+<div role="alert" class="timeout-warning">
   Your session will expire in 2 minutes. 
-  <button onclick="extendSession()">Extend Session</button>
+  <button type="button" onclick="extendSession()">Extend Session</button>
 </div>
 ```