nixos/n8n: fix malformed env vars (#460609)

nixos/modules/services/misc/n8n.nix

@@ -61,7 +61,7 @@ in
             readOnly = true;
           };
           N8N_DIAGNOSTICS_ENABLED = lib.mkOption {
-            type = with lib.types; coercedTo bool toString str;
+            type = with lib.types; coercedTo bool builtins.toJSON str;
             default = false;
             description = ''
               Whether to share selected, anonymous telemetry with n8n.
@@ -69,7 +69,7 @@ in
             '';
           };
           N8N_VERSION_NOTIFICATIONS_ENABLED = lib.mkOption {
-            type = with lib.types; coercedTo bool toString str;
+            type = with lib.types; coercedTo bool builtins.toJSON str;
             default = false;
             description = ''
               When enabled, n8n sends notifications of new versions and security updates.

nixos/tests/n8n.nix

@@ -25,5 +25,6 @@ in
     machine.succeed("grep -qF ${webhookUrl} /etc/systemd/system/n8n.service")
     machine.succeed("grep -qF 'HOME=/var/lib/n8n' /etc/systemd/system/n8n.service")
     machine.fail("grep -qF 'GENERIC_TIMEZONE=' /etc/systemd/system/n8n.service")
+    machine.succeed("grep -qF 'N8N_DIAGNOSTICS_ENABLED=false' /etc/systemd/system/n8n.service")
   '';
 }