samples: cmsis_rtos_v1: philosophers: skip qemu_leon3

SPARC systems take a huge penalty in stack usage due to register window
saves.  A recent patch reverted SPARC-specific increases to various
stack sizes, causing this test to fail.

Other platforms are excluded because of stack limits, so do that here
too.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>