[css-highlight-api] fix: typo: encouraged to user -> encouraged to use (w3c#10351)

Author: matubu

css-highlight-api-1/Overview.bs

@@ -564,7 +564,7 @@ Range Updating and Invalidation</h3>
 		has a significant performance cost.
 		Authors who intend to observe DOM changes and react to them
 		by adjusting or recreating the ranges in their [=custom highlights=]
-		are strongly encouraged to user {{StaticRange}}s
+		are strongly encouraged to use {{StaticRange}}s
 		in order to avoid this costly but unnecessary step.
 
 		Conversely, authors who use {{StaticRange}}s