tests: don't run socat tests on MacOS as well

tests: don't run socat tests on MacOS as well

In preparation for the next patch when we enable socat for our CI
images we need to disable this part of the test for MacOS. The bug has
been raised here:

  https://gitlab.com/qemu-project/qemu/-/issues/1495

Once that is fixed we should re-enable the test.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230228190653.1602033-2-alex.bennee@linaro.org>