testharness: Use right lastStartTag w/ script data

This change ensures that TokenizerTester uses the correct, expected
lastStartTag value from the test source when the initialStates value in
the test source includes “Script data state” — or else if the test
source specifies no lastStartTag, then “script” is used as the value.

Otherwise, without this change, TokenizerTester is hardcoded to always
use “script” as the lastStartTag when running a test case with
“Script data state” as the initial state. That discrepancy causes us to
fail the following case from the html5lib-tests suite:

* https://github.com/html5lib/html5lib-tests/blob/master/tokenizer/domjs.test#L219-L223
  ("lowercase endtags")

Author: sideshowbarker

test-src/nu/validator/htmlparser/test/TokenizerTester.java

@@ -164,8 +164,9 @@ private void runTest(JSONObject test) throws SAXException, IOException {
                     runTestInner(inputString, expectedTokens, description,
                             Tokenizer.PLAINTEXT, lastStartTag);
                 } else if (SCRIPT_DATA.equals(value)) {
+                    lastStartTag = lastStartTag == null ? "script" : lastStartTag;
                     runTestInner(inputString, expectedTokens, description,
-                            Tokenizer.SCRIPT_DATA, "script");
+                            Tokenizer.SCRIPT_DATA, lastStartTag);
                 } else {
                     throw new RuntimeException("Broken test data.");
                 }