tests: make smoke-tests Qt6-safe (use QStringLiteral/QLatin1)

Lts/DDS/DdsUnitTestsPlaceholder/ddsGenericDataTests_smoke.cpp

@@ -6,12 +6,12 @@ class GenericSmokeTest : public QObject {
 private slots:
   void test_string_ops() {
     QString s = QString::fromUtf8("mIxEd");
-    QCOMPARE(s.toLower(), QString("mixed"));
+    QCOMPARE(s.toLower(), QStringLiteral("mixed"));
   }
   void test_basic_qvariant() {
-    QVariant v = QString("value");
+    QVariant v = QStringLiteral("value");
     QVERIFY(v.canConvert<QString>());
-    QCOMPARE(v.toString(), QString("value"));
+    QCOMPARE(v.toString(), QStringLiteral("value"));
   }
 };