fix(ci): register arbiter module via ZEPHYR_EXTRA_MODULES; drop ZTEST_NEW_API

- ZEPHYR_EXTRA_MODULES=\/app tells Zephyr CMake to load
  arbiter's Kconfig and cmake files from the checked-out module path,
  fixing 'undefined symbol ARBITER'
- Remove CONFIG_ZTEST_NEW_API=y from test_arbiter_blob and test_arbiter_eval
  prj.conf; symbol was removed in Zephyr v4.x (new API is now the default)

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: tbitcs

.github/workflows/ci.yml

@@ -61,6 +61,9 @@ jobs:
     env:
       # native_sim uses host GCC; skip cross-compiler toolchain lookup.
       ZEPHYR_TOOLCHAIN_VARIANT: host
+      # app/ is the arbiter module checkout; register it as an extra module
+      # so Zephyr CMake loads its Kconfig and cmake files.
+      ZEPHYR_EXTRA_MODULES: ${{ github.workspace }}/app
     steps:
       - uses: actions/checkout@v4
         with:

tests/unit/test_arbiter_blob/prj.conf

@@ -1,4 +1,3 @@
 CONFIG_ARBITER=y
 CONFIG_ARBITER_BLOB_LOADER=y
 CONFIG_ZTEST=y
-CONFIG_ZTEST_NEW_API=y

tests/unit/test_arbiter_eval/prj.conf

@@ -1,4 +1,3 @@
 CONFIG_ARBITER=y
 CONFIG_ARBITER_TRACE=y
 CONFIG_ZTEST=y
-CONFIG_ZTEST_NEW_API=y