[Glitch] Fix Skeleton placeholders being animated when setting to reduce animations is enabled

Port 4a9460f7bd to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/styles/admin.scss

@@ -1330,6 +1330,10 @@ a.sparkline {
   line-height: 1;
   width: 100%;
   animation: skeleton 1.2s ease-in-out infinite;
+
+  .reduce-motion & {
+    animation: none;
+  }
 }
 
 @keyframes skeleton {