[css-color-4] dedup example ID

Author: svgeesus

css-color-4/Overview.bs

@@ -4469,7 +4469,7 @@ Interpolating with alpha</h3>
 		when premultiplication is undone.
 	</div>
 
-	<div class="example" id="ex-premultiplied-lab">
+	<div class="example" id="ex-premultiplied-lch">
 		To interpolate, in the chroma-preserving LCH colorspace, the same two colors
 		<span class="swatch" style="--color: rgb(76%, 62%, 03%, 0.4)"></span> rgb(76% 62% 03% / 0.4)
 		and