LibWeb: Fix assertion failure when tokenizing JS regex literals

This fixes parsing the following regular expression: /</g;

It also adds a simple script element to the HTMLTokenizer regression
test, which also contains that specific regex.

Tests/LibWeb/TestHTMLTokenizer.cpp

@@ -193,5 +193,5 @@ TEST_CASE(regression)
     auto file_contents = file.value()->read_all();
     auto tokens = run_tokenizer(file_contents);
     u32 hash = hash_tokens(tokens);
-    EXPECT_EQ(hash, 2891738465u);
+    EXPECT_EQ(hash, 2203864459u);
 }