LibWeb: Try to fix a flaky animation test

Not sure if this'll fix it fully, as the flake has only ever been
observed on CI.

Tests/LibWeb/Text/input/WebAnimations/animation-properties/replaceState.html

@@ -16,6 +16,10 @@
         println(`Animation's replaceState is not removed after creating new animation: ${animation1.replaceState === "active"}`);
 
         await animation2.finished;
+
+        // This shouldn't be necessary, but this test has been a bit flaky on CI, so this should hopefully make the test more reliable
+        await animationFrame();
+
         println(`Animation's replaceState is removed after new animation finishes: ${animation1.replaceState === "removed"}`);
     });
 </script>