tests: ztest base: fix board name

Use full board name in cmake file.
Akin to the fix done in #80270
#80270
following the changes from
#77250
In which twister now uses the full board name when calling cmake.

Signed-off-by: Alberto Escolar Piedras <[email protected]>

Author: aescolar

tests/ztest/base/CMakeLists.txt

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 cmake_minimum_required(VERSION 3.20.0)
-if(BOARD STREQUAL unit_testing)
+if(BOARD STREQUAL unit_testing/unit_testing)
   find_package(Zephyr COMPONENTS unittest REQUIRED HINTS $ENV{ZEPHYR_BASE})
   project(base)