style(terraform): adjust indentation for monitoring VM in prod tfvars

Update the indentation of the `virtual_machines` map in `terraform/prod/terraform.tfvars` from 4 spaces to 2 spaces to maintain consistency with the surrounding HCL code style. No functional changes were made to the configuration values.

terraform/prod/terraform.tfvars

@@ -34,15 +34,15 @@ admin_ssh_public_key_path = "~/.ssh/keys/id_rsa.pub"
 default_vm_user = "damien"
 
 virtual_machines = {
-    "monitoring" = {
-        os       = "debian"
-        cores    = 2
-        memory   = 4096
-        disk_gb  = 30
-        ip       = "192.168.1.161"
-        gateway  = "192.168.1.254"
-        tags     = ["monitoring"]
-    }
+  "monitoring" = {
+    os      = "debian"
+    cores   = 2
+    memory  = 4096
+    disk_gb = 30
+    ip      = "192.168.1.161"
+    gateway = "192.168.1.254"
+    tags    = ["monitoring"]
+  }
 }
 
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