QTest::qWaitFor: scope std::chrono using directive tighter

... moving it away from between a comment and the C++ code the comment
pertains to.

Pick-to: 6.7
Change-Id: I56b3ded01d1800bae19121e4b9340d0c43f1da85
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/corelib/kernel/qtestsupport_core.h

@@ -28,8 +28,6 @@ qWaitFor(Functor predicate, QDeadlineTimer deadline = QDeadlineTimer(std::chrono
     // qWait() is expected to spin the event loop at least once, even when
     // called with a small timeout like 1ns.
 
-    using namespace std::chrono;
-
     do {
         // We explicitly do not pass the remaining time to processEvents, as
         // that would keep spinning processEvents for the whole duration if
@@ -43,6 +41,8 @@ qWaitFor(Functor predicate, QDeadlineTimer deadline = QDeadlineTimer(std::chrono
         if (predicate())
             return true;
 
+        using namespace std::chrono;
+
         if (const auto remaining = deadline.remainingTimeAsDuration(); remaining > 0ns)
             qSleep((std::min)(10ms, ceil<milliseconds>(remaining)));