tests: zephyr: drivers: flash: common: run for LM20 DK

With specific fixture.

Signed-off-by: Piotr Kosycarz <piotr.kosycarz@nordicsemi.no>

Author: nordic-piks

tests/zephyr/drivers/flash/common/testcase.yaml

@@ -28,3 +28,15 @@ tests:
       - nrf54l15dk/nrf54l15/cpuapp
     extra_args:
       - DTC_OVERLAY_FILE="boards/nrf54l15dk_nrf54l15_cpuapp_sqspi.overlay"
+  nrf.extended.drivers.flash.common.default:
+    filter: ((CONFIG_FLASH_HAS_DRIVER_ENABLED and not CONFIG_TRUSTED_EXECUTION_NONSECURE)
+      and (dt_label_with_parent_compat_enabled("storage_partition", "fixed-partitions")
+      or dt_label_with_parent_compat_enabled("storage_partition", "nordic,owned-partitions")))
+    platform_allow:
+      - nrf54lm20pdk/nrf54lm20a/cpuapp
+      - nrf54lm20pdk@0.2.0/nrf54lm20a/cpuapp
+      - nrf54lm20pdk@0.2.0.csp/nrf54lm20a/cpuapp
+    integration_platforms:
+      - nrf54lm20pdk/nrf54lm20a/cpuapp
+    harness_config:
+      fixture: external_flash