nixos/mosquitto: fix attribute path display in assertions

nixos/modules/services/networking/mosquitto.nix

@@ -296,7 +296,7 @@ let
   };
 
   listenerAsserts = prefix: listener:
-    assertKeysValid prefix freeformListenerKeys listener.settings
+    assertKeysValid "${prefix}.settings" freeformListenerKeys listener.settings
     ++ userAsserts prefix listener.users
     ++ imap0
       (i: v: authAsserts "${prefix}.authPlugins.${toString i}" v)
@@ -398,7 +398,7 @@ let
   };
 
   bridgeAsserts = prefix: bridge:
-    assertKeysValid prefix freeformBridgeKeys bridge.settings
+    assertKeysValid "${prefix}.settings" freeformBridgeKeys bridge.settings
     ++ [ {
       assertion = length bridge.addresses > 0;
       message = "Bridge ${prefix} needs remote broker addresses";
@@ -527,7 +527,7 @@ let
 
   globalAsserts = prefix: cfg:
     flatten [
-      (assertKeysValid prefix freeformGlobalKeys cfg.settings)
+      (assertKeysValid "${prefix}.settings" freeformGlobalKeys cfg.settings)
       (imap0 (n: l: listenerAsserts "${prefix}.listener.${toString n}" l) cfg.listeners)
       (mapAttrsToList (n: b: bridgeAsserts "${prefix}.bridge.${n}" b) cfg.bridges)
     ];