py: tests: Bind should run only on sandbox

Disable test to run on any other platform than sandbox.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Link: https://lore.kernel.org/r/786bfdfda7dee4494e39c3fff699970ecd623116.1657191142.git.michal.simek@amd.com