LibWeb: Add a test for setting and getting Text data

This is a pretty straightforward test, but I managed to make this crash
on real sites while trying to fix #20971 without any other test in the
existing suite failing.

Tests/LibWeb/Text/expected/DOM/Text-set-get-data.txt

@@ -0,0 +1 @@
+Next 🙃

Tests/LibWeb/Text/input/DOM/Text-set-get-data.html

@@ -0,0 +1,9 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        const str = 'Next 🙃';
+        let text = new Text(str);
+        text.data = str;
+        println(text.data);
+    });
+</script>