AchievementSettings: Move pragma once out of ifdef

Makes the header a little more consistent with others (and also we
should still have a header guard be present at all times).

Source/Core/Core/Config/AchievementSettings.h

@@ -1,9 +1,10 @@
 // Copyright 2023 Dolphin Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
-#ifdef USE_RETRO_ACHIEVEMENTS
 #pragma once
 
+#ifdef USE_RETRO_ACHIEVEMENTS
+
 #include "Common/Config/Config.h"
 
 namespace Config