tests/lib/heap: Disable renode emulator platform
tests/lib/heap: Disable renode emulator platform

The renode emulator is REALLY slow on this test, what completes in 20
seconds on qemu takes 4-10 minutes on renode.  That's causing trouble
in CI.

And this is a CPU-bound unit test of library code, where we have
coverage for riscv32 via qemu anyway.  There's no value to having
better platform emulation here.

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

nashif/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,nashif/zephyr,finikorg/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr