tst_QMutex[qnx]: increase system timer resolution

I don't know what it is but it's not 1, because it is quite
often flaky in these tests. A single failure leads to deadlock
that takes 5 minutes to fail. Then a rerun might do another
5 minutes and fail the integration, or it will pass but take
longer to do so.

Pick-to: 6.5
Change-Id: I188276df7800b00a20dbe39edee91c582f0a82a7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 6aee3342e9d0829bb113583c2b6ecc6c94492d2c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 3789e5972e6b244fe2e1f80fc794548302ae16b9)

tests/auto/corelib/thread/qmutex/tst_qmutex.cpp

@@ -61,6 +61,8 @@ static QSemaphore threadsTurn;
 enum {
 #ifdef Q_OS_WIN
     systemTimersResolution = 16,
+#elif defined(Q_OS_QNX)
+    systemTimersResolution = 10,
 #else
     systemTimersResolution = 1,
 #endif