tst_QByteArray: add Qt::StringLiterals to the namespace scope

... and remove all previous function-level occurrences.

Pick-to: 6.5
Change-Id: I90df40922e3aed15efc04e885d9f54c577a948b6
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

tests/auto/corelib/text/qbytearray/tst_qbytearray.cpp

@@ -12,6 +12,8 @@
 
 #include "../shared/test_number_shared.h"
 
+using namespace Qt::StringLiterals;
+
 class tst_QByteArray : public QObject
 {
     Q_OBJECT
@@ -2189,7 +2191,6 @@ void tst_QByteArray::literals()
 void tst_QByteArray::userDefinedLiterals()
 {
     {
-        using namespace Qt::StringLiterals;
         QByteArray str = "abcd"_ba;
 
         QVERIFY(str.size() == 4);