Add job to make input env var

Author: dsotirakis

actions/push-to-gar-docker-multi-arch/action.yaml

@@ -3,15 +3,26 @@ description: Composite action to push to Google Artifact Registry
 on:
   workflow_call:
     inputs:
-      platform_string:
+      platforms:
         description: desc
         required: true
         type: string
 
+env:
+  platform_env: ${{ inputs.platforms }}
+
 jobs:
+  expose-env-var:
+    runs-on: ubuntu-latest
+    outputs:
+      platforms: ${{ env.platform_env }}
+    steps:
+      - run: echo "exposing env var"
+
   resolve-platforms:
+    needs: [expose-env-var]
     runs-on: ubuntu-latest
     steps:
       - uses: ./actions/resolve-architectures
         with: 
-          platforms: "${{ github.event.inputs.platform_string }}"
+          platforms: ${{ needs.expose-env-var.outputs.platforms }}