tests/ztest/fail: fix board name

Use full board name in cmake file.
Akin to the fix done in
https://github.com/zephyrproject-rtos/zephyr/pull/80270/
following the changes from
https://github.com/zephyrproject-rtos/zephyr/pull/77250/

Note after the Zephyr cmake code has been run the BOARD
variable is split into BOARD BOARD_QUALIFIERS,
where BOARD does not contain the qualifiers anymore
(see cmake/modules/boards.cmake for more info).

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

tests/ztest/fail/CMakeLists.txt

@@ -4,7 +4,7 @@
 cmake_minimum_required(VERSION 3.20.0)
 include(ExternalProject)
 
-if(BOARD STREQUAL unit_testing)
+if(BOARD STREQUAL unit_testing/unit_testing)
   find_package(Zephyr COMPONENTS unittest REQUIRED HINTS $ENV{ZEPHYR_BASE})
   set(target testbinary)
   # Set the target binary for the 'core' external project. The path to this must match the one set
@@ -36,7 +36,7 @@ string(REPLACE ";" " " fail_test_config "${fail_test_config}")
 ExternalProject_Add(core
     SOURCE_DIR ${CMAKE_CURRENT_LIST_DIR}/core
     CMAKE_ARGS
-      -DBOARD:STRING=${BOARD}
+      -DBOARD:STRING=${BOARD}${BOARD_QUALIFIERS}
       -DCMAKE_INSTALL_PREFIX:PATH=${CMAKE_BINARY_DIR}/core
       ${fail_test_config}
 )

tests/ztest/fail/core/CMakeLists.txt

@@ -23,7 +23,7 @@ elseif(CONFIG_ZTEST_FAIL_TEST_UNEXPECTED_ASSUME)
   list(APPEND test_sources src/unexpected_assume.cpp)
 endif()
 
-if(BOARD STREQUAL unit_testing)
+if(BOARD STREQUAL unit_testing/unit_testing)
   find_package(Zephyr COMPONENTS unittest REQUIRED HINTS $ENV{ZEPHYR_BASE})
   project(base)