update terraform backend config file path

Author: ale210

.github/workflows/terraform-apply.yaml

@@ -32,4 +32,4 @@ jobs:
       uses: dflook/terraform-apply@v1
       with:
         path: terraform
-        backend_config_file: prod.backend.tfvars
+        backend_config_file: terraform/prod.backend.tfvars

.github/workflows/terraform-plan.yaml

@@ -32,4 +32,4 @@ jobs:
       uses: dflook/terraform-plan@v1
       with:
         path: terraform
-        backend_config_file: prod.backend.tfvars
+        backend_config_file: terraform/prod.backend.tfvars