task: checkout generated-terraform branch to a nested folder

Part of #1631

[skip ci]

Author: php-coder

.github/workflows/provision-by-terraform.yml

@@ -28,6 +28,11 @@ jobs:
           # Whether to configure the token or SSH key with the local git config. Default: true
           persist-credentials: false
 
+      - name: Checkout terraform data to a subdirectory
+        run: |
+          git fetch --depth=1 origin generated-terraform
+          git worktree add terraform-data generated-terraform
+
       # https://github.com/tfutils/tfenv#manual
       - name: Install tfenv
         uses: actions/[email protected]
@@ -63,3 +68,8 @@ jobs:
       - name: Run terraform plan
         working-directory: infra/terraform
         run: terraform plan -detailed-exitcode
+
+      - name: Cleanup
+        if: always()
+        run: |
+          [ ! -d terraform-data ] || git worktree remove terraform-data