CCM-10193 use GitHub App token

Signed-off-by: Tim Ireland <tim.ireland@hscic.gov.uk>

Author: timireland

.github/workflows/stage-3-build.yaml

@@ -95,6 +95,8 @@ jobs:
     env:
       PROXYGEN_API_NAME: nhs-notify-supplier
       PR_NUMBER: ${{ inputs.pr_number }}
+      APP_CLIENT_ID: ${{ secrets.APP_CLIENT_ID }}
+      APP_PEM_FILE: ${{ secrets.APP_PEM_FILE }}
     steps:
       - name: "Checkout code"
         uses: actions/checkout@v4