make script posix compliant

action.yaml

@@ -39,6 +39,8 @@ runs:
 
     - name: Build and Push with Kaniko
       shell: sh
+      env:
+        INPUT_BUILD_ARGS: ${{ inputs.build_args }}
       run: |
         # 1. Initialize Kaniko Docker config directory
         mkdir -p /kaniko/.docker
@@ -61,11 +63,9 @@ runs:
         fi
 
         DYNAMIC_BUILD_ARGS=""
-        if [ -n "${{ inputs.build_args }}" ]; then
-            for arg in ${{ inputs.build_args }}; do
-                DYNAMIC_BUILD_ARGS="$DYNAMIC_BUILD_ARGS --build-arg=$arg"
-            done
-        fi
+        for arg in $INPUT_BUILD_ARGS; do
+          DYNAMIC_BUILD_ARGS="$DYNAMIC_BUILD_ARGS --build-arg=$arg"
+        done 
 
         # 5. Fire Kaniko executor
         /kaniko/executor \