message: Fix test for desktopWallpaper
  This fixes the test for when we switched `"DesktopWallpaper"` to `"desktopWallpaper"`
diff: @@ -1410,14 +1410,14 @@ namespace SettingsModelLocalTests
  }
  void DeserializationTests::TestProfileBackgroundImageWithDesktopWallpaper()
  {
  - const winrt::hstring expectedBackgroundImagePath{ winrt::to_hstring("DesktopWallpaper") };
  + const winrt::hstring expectedBackgroundImagePath{ L"desktopWallpaper" };
  const std::string settingsJson{ R"(
  {
  "profiles": [
  {
  "name": "profile0",
  - "backgroundImage": "DesktopWallpaper"
  + "backgroundImage": "desktopWallpaper"
  }
  ]
  })" };
  