tests: code_relocation: exclude mr_canhubk3 board

The mr_canhubk3 board enables by default an off-chip watchdog that must
be serviced to avoid triggering a reset and cannot be disabled on a
per-test basis. The watchdog driver make uses of a semaphore during
device init and on this test the relocation of the kernel sources
produces a fault. So skip this test for this board.

Signed-off-by: Manuel Argüelles <manuel.arguelles@nxp.com>