Fix flaky forced colors test

fast/css/forced-colors-mode/forced-colors-mode-12.html was detected as
flaky. This tests animations in forced colors mode. Looking at other
animation tests, it looks like the issue was that I needed to add
"media="screen"" to the style element.

Bug: 994465
Change-Id: I982343bf05e3aa4ac4df2caab0373103f5165cb4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1758706Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Alison Maher <almaher@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#688316}

third_party/blink/web_tests/fast/css/forced-colors-mode/forced-colors-mode-12.html

@@ -4,7 +4,7 @@
     Forced colors mode - animations.
     Tests that animation colors are overridden in forced colors mode.
   </title>
-  <style type="text/css">
+  <style type="text/css" media="screen">
     #forcedtextcolor {
       color: WindowText;
       forced-color-adjust: none;
@@ -26,7 +26,7 @@
   <p id="forcedtextcolor"></p>
 </body>
 
-<script src="../../../animations/resources/animation-test-helpers.js"></script>
+<script src="../../../animations/resources/animation-test-helpers.js" type="text/javascript" charset="utf-8"></script>
 <script type="text/javascript" charset="utf-8">
   var textcolor = getComputedStyle(forcedtextcolor).color;
   const expectedValues = [