tests/ztest/fail: Fix build for native_sim

The final executable output from the native_sim
(or native_posix) build is zephyr.exe
(in native_posix zephyr.elf happened to be just a copy of
the exe, but in native_sim it is an intermediate build step)

So we need to use the exe instead.

Note: As the exe is generated with a custom target, we need
to install it using install(FILES), which also requires the
destination and permissions to be listed manually. The
permissions set are just the cmake default permissions
for install(PROGRAMS).

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