[css-text-4] list <string> in the definition of text-align-all

This had been forgotten in the edit that introduced it to the shorthand.

See #9386

Author: frivoal

css-text-4/Overview.bs

@@ -8809,7 +8809,7 @@ Default Text Alignment: the 'text-align-all' property</h3>
 
 	<pre class="propdef">
 	Name: text-align-all
-	Value: start | end | left | right | center | justify | match-parent
+	Value: start | end | left | right | center | <<string>> | justify | match-parent
 	Initial: start
 	Applies to: block containers
 	Inherited: yes