[css-borders-4][editorial] Fix syntax rewrite mistake (#12844)

Author: cdoublev

css-borders-4/Overview.bs

@@ -699,7 +699,7 @@ The 'corner-top-left', 'corner-top-right',
 	<pre class=propdef>
 		Name: corner-top-left, corner-top-right, corner-bottom-left, corner-bottom-right,
 			corner-start-start, corner-start-end, corner-end-start, corner-end-end
-		Value: <<'border-top-left-radius'>>{1,2} || <<'corner-top-left-shape'>>
+		Value: <<'border-top-left-radius'>> || <<'corner-top-left-shape'>>
 		Initial: 0
 		Applies to: all elements (but see prose)
 		Inherited: no