clang-tidy: mark unused ioc field in test stub

The 'ioc' field in DbusSensorObject test stub is intentionally
unused but retained to align with the base implementation.

Marked it with [[maybe_unused]] to suppress clang-tidy's
-Wunused-private-field warning while preserving interface
consistency for future compatibility.

Error details:
'''
tests/src/stubs/dbus_sensor_object.cpp:17:5: error:
    class ‘stubs::DbusSensorObject’ does not have any field named ‘ioc’
   17 |     ioc(ioc), bus(bus), objServer(objServer)
'''

Change-Id: Id86a671b255f98ea22fddca82c24ad2192727235
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>
diff --git a/tests/src/stubs/dbus_sensor_object.hpp b/tests/src/stubs/dbus_sensor_object.hpp
index 45ee4c7..3192630 100644
--- a/tests/src/stubs/dbus_sensor_object.hpp
+++ b/tests/src/stubs/dbus_sensor_object.hpp
@@ -30,7 +30,7 @@
     static constexpr Properties property = {};
 
   private:
-    boost::asio::io_context& ioc;
+    [[maybe_unused]] boost::asio::io_context& ioc;
     std::shared_ptr<sdbusplus::asio::connection> bus;
     std::shared_ptr<sdbusplus::asio::object_server> objServer;