`winget validate` does not recognize `$schema` field for JSON manifests

Brief description of your issue

winget validate throws warnings when the $schema field is defined for JSON manifests.

Steps to reproduce

Taking an example of singleton manifest for easier repro, but the same applies for multifile manifests

{
"$schema": "https://aka.ms/winget-manifest.singleton.1.5.0.schema.json",
"PackageIdentifier": "jqlang.jq",
"PackageVersion": "1.2.3",
"PackageLocale": "en-US",
"Publisher": "TestPublisher",
"PackageName": "Full Singleton 1.5 Test",
"PackageUrl": "https://fakeTestUrl.com",
"License": "MIT",
"ShortDescription": "A manifest used to verify that all fields from a full 1.5 singleton manifest can be deserialized and updated.",
"Installers": [
    {
        "MinimumOSVersion": "10.0.0.0",
        "Architecture": "x64",
        "InstallerUrl": "https://fakedomain.com/WingetCreateTestExeInstaller.exe",
        "InstallerType": "inno",
        "InstallerSha256": "A7803233EEDB6A4B59B3024CCF9292A6FFFB94507DC998AA67C5B745D197A5DC"
    }
],
"ManifestType": "singleton",
"ManifestVersion": "1.5.0"
}

Expected behavior

Manifest validation succeeds with no warnings.

Actual behavior

 ~/1.2.3 winget validate --manifest .
Manifest validation succeeded with warnings.
Manifest Warning: Unknown field. [$schema] Line: 3, Column: 1

Environment

Windows Package Manager (Preview) v1.7.3481-preview
Copyright (c) Microsoft Corporation. All rights reserved.

Windows: Windows.Desktop v10.0.22621.3007
System Architecture: X64
Package: Microsoft.DesktopAppInstaller v1.22.3481.0

Winget Directories
-------------------------------------------------------------------------------------------------------------------------------
Logs                               %LOCALAPPDATA%\Packages\Microsoft.DesktopAppInstaller_8wekyb3d8bbwe\LocalState\DiagOutputDir
User Settings                      %LOCALAPPDATA%\Packages\Microsoft.DesktopAppInstaller_8wekyb3d8bbwe\LocalState\settings.json
Portable Links Directory (User)    %LOCALAPPDATA%\Microsoft\WinGet\Links
Portable Links Directory (Machine) C:\Program Files\WinGet\Links
Portable Package Root (User)       %LOCALAPPDATA%\Microsoft\WinGet\Packages
Portable Package Root              C:\Program Files\WinGet\Packages
Portable Package Root (x86)        C:\Program Files (x86)\WinGet\Packages
Installer Downloads                %USERPROFILE%\Downloads

Links
---------------------------------------------------------------------------
Privacy Statement   https://aka.ms/winget-privacy
License Agreement   https://aka.ms/winget-license
Third Party Notices https://aka.ms/winget-3rdPartyNotice
Homepage            https://aka.ms/winget
Windows Store Terms https://www.microsoft.com/en-us/storedocs/terms-of-sale

Admin Setting                             State
--------------------------------------------------
LocalManifestFiles                        Enabled
BypassCertificatePinningForMicrosoftStore Disabled
InstallerHashOverride                     Enabled
LocalArchiveMalwareScanOverride           Disabled

Start by reproducing the warning with the provided singleton manifest and winget validate --manifest ., then trace the CLI's manifest-validation path for handling of JSON fields. Done means $schema is accepted for singleton and multifile manifests and validation succeeds without the reported warning.