[infra] Update DefaultVersions.props package versions

[github-actions]

Caution

Protected files were modified in this change.
This pull request is in request_review mode and requires explicit human scrutiny before merge.

Protected files: Directory.Packages.props

Automated update of toolset package versions in src/Microsoft.DotNet.Arcade.Sdk/tools/DefaultVersions.props (and Directory.Packages.props kept in sync).

Summary of changes

Property	Package ID	Old version	New version	Feed
MicrosoftNETTestSdkVersion	Microsoft.NET.Test.Sdk	18.0.1	18.9.0	nuget.org
MicrosoftTestPlatformVersion	Microsoft.TestPlatform	18.0.1	18.9.0	nuget.org
XUnitAnalyzersVersion	xunit.analyzers	2.0.0-pre.51	2.0.0	nuget.org
XUnitRunnerVisualStudioVersion	xunit.runner.visualstudio	4.0.0-pre.4	4.0.0	nuget.org
XUnitV3Version	xunit.v3	4.0.0-pre.81	4.0.0	nuget.org
MicrosoftTestingPlatformVersion	Microsoft.Testing.Platform	2.2.3	2.3.3	nuget.org
MSTestVersion	MSTest	4.2.3	4.3.3	nuget.org
MicrosoftVSSDKBuildToolsDefaultVersion	Microsoft.VSSDK.BuildTools	17.14.2120	18.9.820	nuget.org
MicroBuildPluginsSwixBuildVersion	MicroBuild.Plugins.SwixBuild	1.0.422	1.1.37	dotnet-eng
MicrosoftVisualStudioEngMicroBuildPluginsSwixBuildVersion	Microsoft.VisualStudioEng.MicroBuild.Plugins.SwixBuild	1.1.286	1.1.973	dotnet-eng
MicrosoftSignedWixVersion	Microsoft.Signed.Wix	3.14.1-9323.2545153	3.14.1-11131.2940454	dotnet-eng
MicrosoftWixToolsetSdkVersion	Microsoft.WixToolset.Sdk	6.0.3-dotnet.6	6.0.3-dotnet.14	dotnet-eng

Directory.Packages.props was also updated to keep the xunit/testing-platform overrides in sync with DefaultVersions.props.

Packages needing mirroring

⚠️ The build is expected to fail until the packages below are mirrored to the dotnet-public feed. See Documentation/MirroringPackages.md for instructions.

Package ID	Version
Microsoft.NET.Test.Sdk	18.9.0
Microsoft.TestPlatform	18.9.0
xunit.analyzers	2.0.0
xunit.runner.visualstudio	4.0.0
xunit.v3	4.0.0
Microsoft.Testing.Platform	2.3.3
MSTest	4.3.3
Microsoft.VSSDK.BuildTools	18.9.820

Generated by 📦 Update DefaultVersions.props · sonnet46 2.2M · ◷

[github-actions]

Protected files were modified in this pull request and require manual scrutiny before merge.

Please verify that each protected-file change is intentional, policy-compliant, and safe:

• Protected files: Directory.Packages.props