Update long running test workflow to use GH token for terraform priva…

…te registry (radius-project#7545)

# Description

Long-running tests are failing during the Terraform private registry
step. This PR updates the long running test workflow to use a GH token
to authenticate to the Terraform private registry

## Type of change

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- This pull request is a minor refactor, code cleanup, test improvement,
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Fixes: #issue_number

Signed-off-by: sk593 <[email protected]>

.github/workflows/long-running-azure.yaml

@@ -78,6 +78,9 @@ env:
   # The valid radius build time window in seconds to rebuild radius. 24 hours = 24 * 60 * 60 = 86400
   VALID_RADIUS_BUILD_WINDOW: 86400
 
+  # The functional test GitHub app id
+  FUNCTIONAL_TEST_APP_ID: 425843
+
   # The AKS cluster name
   AKS_CLUSTER_NAME: "radlrtest00-aks"
   # The resource group for AKS_CLUSTER_NAME resource.
@@ -109,6 +112,12 @@ jobs:
       CHECKOUT_REF: ${{ steps.gen-id.outputs.CHECKOUT_REF }}
       RAD_CLI_ARTIFACT_NAME: ${{ steps.gen-id.outputs.RAD_CLI_ARTIFACT_NAME }}
     steps:
+      - name: Get GitHub app token
+        uses: tibdex/github-app-token@v2
+        id: get_installation_token
+        with: 
+          app_id: ${{ env.FUNCTIONAL_TEST_APP_ID }}
+          private_key: ${{ secrets.FUNCTIONAL_TEST_APP_PRIVATE_KEY }}
       - name: Restore the latest cached binaries
         uses: actions/cache/restore@v4
         with:
@@ -306,6 +315,7 @@ jobs:
       AZURE_TEST_RESOURCE_GROUP: radtest-${{ needs.build.outputs.UNIQUE_ID }}-e2e-all
       RAD_CLI_ARTIFACT_NAME: ${{ needs.build.outputs.RAD_CLI_ARTIFACT_NAME }}
       BICEP_RECIPE_TAG_VERSION: ${{ needs.build.outputs.REL_VERSION }}
+      GH_TOKEN: ${{ steps.get_installation_token.outputs.token }}
     steps:
       - name: Checkout
         uses: actions/checkout@v4