[pointer-animations-1] Link source and target back to right type (w3c#13225)

The values are for the `<timeline-range-center-subject>` type but the wrapping
`<>` were missing.

Author: tidoust

pointer-animations-1/Overview.bs

@@ -437,7 +437,7 @@ spec:selectors-4; type:dfn; text:selector
 	which indicates a [=CSS identifier=] representing
 	one of the following:
 
-	<dl dfn-type=value dfn-for="timeline-range-center-subject">
+	<dl dfn-type=value dfn-for="<timeline-range-center-subject>">
 		<dt><dfn>source</dfn>
 		<dd>
 			The element whose [=pointer offset=]