LibWeb: Set the correct prototype for SVGAElement instances

Author: https://github.com/awesomekling
Commit: 4db05ecf69
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/304
Reviewed-by: https://github.com/nico ✅

Tests/LibWeb/Text/input/SVG/a-element-prototype.html

@@ -0,0 +1,7 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        let a = document.createElementNS("http://www.w3.org/2000/svg", "a");
+        println(a.__proto__ === SVGAElement.prototype);
+    });
+</script>