tests: add ironside variant to all nRF54H20 tests

Ref: NCSDK-32229
Signed-off-by: Håkon Amundsen <[email protected]>

Author: hakonfam

tests/drivers/spi/spi_loopback/testcase.yaml

@@ -262,6 +262,7 @@ tests:
       - EXTRA_DTC_OVERLAY_FILE="boards/nrf_at_32mhz.overlay"
     platform_allow:
       - nrf54h20dk/nrf54h20/cpuapp
+      - nrf54h20dk/nrf54h20/cpuapp/iron
   drivers.spi.nrf54h_fast_8mhz_port2:
     extra_args:
       - DTC_OVERLAY_FILE="boards/nrf54h20dk_nrf54h20_cpuapp_fast_p2.overlay"