Remove dead variable and add concurrency guard

- Remove unused network_name variable in configure-azure-credentials
  "Get Azure client id" step (only account_name is used)
- Add concurrency key per network to prevent overlapping terraform
  applies against the same state

Author: Sean Thomas

.github/actions/configure-azure-credentials/action.yml

@@ -53,7 +53,6 @@ runs:
       run: |
         echo "::group::Azure account authentication details"
 
-        network_name="${{ steps.get-network-name.outputs.network_name }}"
         account_name="${{ steps.get-account-name.outputs.account_name }}"
 
         terraform -chdir=infra/project-config init > /dev/null

.github/workflows/renew-tls-certificates.yml

@@ -20,6 +20,7 @@ jobs:
   renew-certs:
     name: Renew certs (${{ matrix.network_name }})
     runs-on: ubuntu-latest
+    concurrency: renew-tls-certs-${{ matrix.network_name }}
     strategy:
       fail-fast: false
       matrix: