pthread_yield() has been removed in newer linux distros

pthread_yield() is a non-posix extension and was deprecated for a long time.
It's been removed recently at least from Fedora 35. Use sched_yield() instead.

Change-Id: Iae47fa09cc89005aa466446149be87e1b673c074
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

tests/auto/network/socket/qtcpsocket/tst_qtcpsocket.cpp

@@ -2221,7 +2221,7 @@ public slots:
 #if defined(Q_OS_MAC)
         pthread_yield_np();
 #elif defined Q_OS_LINUX && !defined Q_OS_ANDROID
-        pthread_yield();
+        sched_yield();
 #endif
         if (!sock->waitForConnected()) {
             networkTimeout = true;