Set ZEPHIR_BASE for the action

This should help west find back the workspace if the manufest is under
multiple subdirectories.

Signed-off-by: Fabio Baltieri <[email protected]>

Author: fabiobaltieri

action.yml

@@ -32,6 +32,8 @@ inputs:
 
 runs:
   using: "composite"
+  env:
+    ZEPHIR_BASE: ${{ inputs.app-path }}
   steps:
     - name: Install dependencies
       shell: bash