tst_QTcpServer: add missing const

So the array itself is also const.

Amends a94731c2ad85f9dd40050a780f67c911bf12668e.

Change-Id: Ic4d78d3d059dd47f776ffffdd0971b1aa35a69e9
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
(cherry picked from commit 8500e730406cf592d9eeffadab3c4f7e6a51da96)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

tests/auto/network/socket/qtcpserver/crashingServer/main.cpp

@@ -27,7 +27,7 @@ int main(int argc, char *argv[])
             // let's see if we can find the process that would be holding this
             // still open
 #ifdef Q_OS_LINUX
-            static const char *ss_args[] = {
+            static const char *const ss_args[] = {
                 "ss", "-nap", "sport", "=", argv[1], nullptr
             };
             dup2(STDERR_FILENO, STDOUT_FILENO);