tests/subsys/ipc/pbuf: Filter out partial native/posix arch builds

Some AMP native simulator targets (like the nrf5340bsim net core)
will not produce a final executable if only one of the core images
is built, when IPC is enabled, as those images require the other
core image to be able to link.
So this test cannot be run when targetting that core alone
(without using sysbuild to build the other).

Let's filter out these targets to avoid twister building
but finding itself with no executable and error out badly
as it cannot run the test.

The filter condition is effectively:
If building for a native target, there must be an .exe being
produced.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>