Fix grammar typo in prefers-contrast advisement (w3c#5739)

Author: fuzzbomb

mediaqueries-5/Overview.bs

@@ -2669,7 +2669,7 @@ Detecting the desire for increased or decreased color contrast from elements on
 			See [[css-color-adjust-1#forced]] for details.
 
 			<div class=advisement>
-				This does <em>not</em> necessarily indicates
+				This does <em>not</em> necessarily indicate
 				a preference for more contrast.
 				The colors have been forcibly adjusted
 				to match the preference of the user,