(MAINT) Add authorized account for live branch targeting (#312)

Prior to this change, the GHA workflow for checking authorization on submitting PRs to the `live` branch didn't include the `authorized_accounts` parameter.

When you retrieve the permissions for the `learn-build-service-prod[bot]` account, the API reports that the automation account lacks all permissions.

This change adds the bot account to an allow-list to prevent the error.

Author: michaeltlombardi

.github/workflows/targeting-valid-branch.yml

@@ -20,3 +20,4 @@ jobs:
         uses: MicrosoftDocs/PowerShell-Docs/.github/actions/verification/authorization/v1@main
         with:
           token: ${{ github.token }}
+          authorized_accounts: learn-build-service-prod[bot]