.github/workflows: Use tianocore-assign-reviewers [bot] app

Update workflow to generate a token so the assign reviewers
action runs with the name and permissions of the
tianocore-assign-reviewers [bot] application.

Signed-off-by: Michael D Kinney <[email protected]>

Author: mdkinney

.github/workflows/AssignReviewers.yml

@@ -20,6 +20,13 @@ jobs:
     steps:
       - name: Checkout Pull Request Target
         uses: actions/checkout@v2
+      - name: Get Token
+        id: get_workflow_token
+        uses: peter-murray/workflow-application-token-action@v1
+        with:
+          application_id: ${{ secrets.APPLICATION_ID }}
+          application_private_key: ${{ secrets.APPLICATION_PRIVATE_KEY }}
+          organization: tianocore
       - uses: mdkinney/github-action-assign-reviewers@main
         with:
-          token: ${{secrets.CODEOWNERS_VALIDATOR_TOKEN}}
+          token: ${{ steps.get_workflow_token.outputs.token }}