Add TestStringTable test

The TestStringTable tests the fix provided for a crash in StringTable
on shutdown.

Amends: f4ab1279fd

Task-number: QTCREATORBUG-25417
Change-Id: I5a4a7e4a20e1b9611682a976d38dee17d4603c5c
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/autotest/autotestunittests.h

@@ -55,6 +55,7 @@ private slots:
     void testCodeParserGTest_data();
     void testCodeParserBoostTest();
     void testCodeParserBoostTest_data();
+    void testStringTable();
 
 private:
     TestTreeModel *m_model = nullptr;