[css-values-5] Make color-mix() accept 1+ arguments #11530 (#12265)

Oversight in 85cd6d2.

Author: cdoublev

css-values-5/Overview.bs

@@ -998,7 +998,7 @@ Interpolated Color Values: the ''color-mix()'' notation</h3>
 	<pre class=prod>
 		<<color-mix()>> =
 		  color-mix( [ <<progress>> && <<color-interpolation-method>>? ] , <<color>>, <<color>> ) |
-		  color-mix( <<color-interpolation-method>>, [<<color>> && <<percentage [0,100]>>?]#{2} )
+		  color-mix( <<color-interpolation-method>>, [<<color>> && <<percentage [0,100]>>?]# )
 	</pre>
 
 	The used value of the first [=mix notation=] variant