Fix test for highlight pseudos and visited links

In r990326 we added a test for visited links on highlight pseudos,
but it was wrong.

Browsers use the alpha channel from the unvisited styles,
so by default the unvisited style background is transparent,
so you get a transparent background for the visited styles too
(even if you specify something different for them).

We're adding a solid background color to the unvisited style,
so the visited background color is used.

Bug: 1314629
Change-Id: I5ebb789388dc239b09f87a9e21ac5fd53f1113fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3580511
Reviewed-by: Delan Azabani <dazabani@igalia.com>
Commit-Queue: Manuel Rego <rego@igalia.com>
Cr-Commit-Position: refs/heads/main@{#991442}

Author: mrego

css/css-pseudo/target-text-008.html

@@ -6,6 +6,9 @@
 <meta name="assert" content="Checks that ::target-text pseudo-element can be applied on visited links.">
 <link rel="match" href="target-text-008-ref.html">
 <style>
+  a::target-text {
+    background: red;
+  }
   a:visited::target-text {
     color: lime;
     background: green;