fix(build): Use module load approach if found.

* If we detect we're building a Zephyr module, use the module
  define to add it to the build instead of ZMK_CONFIG.

.github/workflows/build-user-config.yml

@@ -66,10 +66,15 @@ jobs:
           shield: ${{ matrix.shield }}
           artifact_name: ${{ matrix.artifact-name }}
         run: |
-          ls zephyr/
-          if [ -e zephyr/module.yml ]; then export zmk_extra_modules_arg=" -DZMK_EXTRA_MODULES='$(pwd)'"; fi
+          if [ -e zephyr/module.yml ]; then
+            export zmk_load_arg="-DZMK_EXTRA_MODULES='${GITHUB_WORKSPACE}'"
+          else
+            export zmk_load_arg="-DZMK_CONFIG='${GITHUB_WORKSPACE}/${{ inputs.config_path }}'"
+          fi
+
+          echo "load_arg=${zmk_load_arg}" >> $GITHUB_ENV
           echo "zephyr_version=${ZEPHYR_VERSION}" >> $GITHUB_ENV
-          echo "extra_cmake_args=${shield:+-DSHIELD=\"$shield\"}${zmk_extra_modules_arg}" >> $GITHUB_ENV
+          echo "extra_cmake_args=${shield:+-DSHIELD=\"$shield\"}" >> $GITHUB_ENV
           echo "display_name=${shield:+$shield - }${board}" >> $GITHUB_ENV
           echo "artifact_name=${artifact_name:-${shield:+$shield-}${board}-zmk}" >> $GITHUB_ENV
 
@@ -102,7 +107,7 @@ jobs:
 
       - name: West Build (${{ env.display_name }})
         shell: sh -x {0}
-        run: west build -s zmk/app -d "${{ env.build_dir }}" -b "${{ matrix.board }}" -- -DZMK_CONFIG="${GITHUB_WORKSPACE}/${{ inputs.config_path }}" ${{ env.extra_cmake_args }} ${{ matrix.cmake-args }}
+        run: west build -s zmk/app -d "${{ env.build_dir }}" -b "${{ matrix.board }}" -- ${{ env.load_arg }} ${{ env.extra_cmake_args }} ${{ matrix.cmake-args }}
 
       - name: ${{ env.display_name }} Kconfig file
         run: |