fix: use legacy S3 backend syntax for Terraform compatibility

Replace 'endpoints' block with 'endpoint' string and remove
unsupported arguments for older Terraform versions.

terraform/prod/providers.tf

@@ -21,17 +21,12 @@ terraform {
     bucket   = "netlab-terraform-backend"
     key      = "prod/terraform.tfstate"
     region   = "fr-par"
-
-    endpoints = {
-      s3 = "https://s3.fr-par.scw.cloud"
-    }
+    endpoint = "https://s3.fr-par.scw.cloud"
 
     # Paramètres requis pour Scaleway (non-AWS S3)
     skip_credentials_validation = true
     skip_region_validation      = true
-    skip_requesting_account_id  = true
     skip_metadata_api_check     = true
-    skip_s3_checksum            = true
   }
 
   required_providers {