Sync xunit v3 versions in Directory.Packages.props with DefaultVersions.props

[Copilot]

Commit 4e3c44c updated xunit v3 versions in DefaultVersions.props but missed the corresponding hardcoded overrides in Directory.Packages.props, which exist because Arcade doesn't consume a live Arcade SDK.

• XUnitV3Version: 3.1.0 → 3.2.2
• XUnitRunnerVisualStudioVersion: 3.1.3 → 3.1.5
• Added MicrosoftTestingPlatformVersion: 1.9.1 override (required by xunit.v3.mtp-v1 3.2.2, which depends on Microsoft.Testing.Platform 1.9.1 — without this override the pinned Arcade SDK in global.json provides the older 1.8.5 version, causing CS1705 build failures)
• Updated comment in Directory.Packages.props to mention MicrosoftTestingPlatformVersion as a property that must be kept in sync
• Updated Documentation/update-xunit.md step 2 to list XUnitV3Version and MicrosoftTestingPlatformVersion with a note about their compatibility dependency

To double check:

• The right tests are in and the right validation has happened. Guidance: https://github.com/dotnet/arcade/blob/main/Documentation/Validation.md

Original prompt

Commit 4e3c44c ("Update xunit.v3 to latest (#16545)") updated xunit v3 versions in src/Microsoft.DotNet.Arcade.Sdk/tools/DefaultVersions.props but missed updating the corresponding hardcoded values in Directory.Packages.props.

Per the instructions in Documentation/update-xunit.md (step 3), hardcoded values in Directory.Packages.props must be kept in sync with DefaultVersions.props.

The following two properties in Directory.Packages.props (lines 18 and 21) need to be updated:

1. XUnitV3Version (line 18): Change from 3.1.0 to 3.2.2
2. XUnitRunnerVisualStudioVersion (line 21): Change from 3.1.3 to 3.1.5

The comment on lines 15-16 of that file explicitly states:

<!-- Overwrite XUnitVersion/XUnitAnalyzersVersion/XUnitRunnerConsoleVersion/XUnitRunnerVisualStudioVersion that comes from the Arcade SDK to be in sync as Arcade doesn't use a live Arcade SDK.
     Keep in sync with DefaultVersions.props. -->

No other files need changes — SendingJobsToHelix.md only references xUnit v2 versions which were not changed.

This pull request was created from Copilot chat.

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[akoeplinger]

@copilot investigate and fix the build failure:

CSC(0,0): error CS1705: (NETCORE_ENGINEERING_TELEMETRY=Build) Assembly 'xunit.v3.mtp-v1' with identity 'xunit.v3.mtp-v1, Version=3.2.2.0, Culture=neutral, PublicKeyToken=8d05b1bb7a6fdb6c' uses 'Microsoft.Testing.Platform, Version=1.9.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' which has a higher version than referenced assembly 'Microsoft.Testing.Platform' with identity 'Microsoft.Testing.Platform, Version=1.8.5.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

CSC(0,0): error CS1705: (NETCORE_ENGINEERING_TELEMETRY=Build) Assembly 'Microsoft.Testing.Extensions.Telemetry' with identity 'Microsoft.Testing.Extensions.Telemetry, Version=1.9.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' uses 'Microsoft.Testing.Platform, Version=1.9.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' which has a higher version than referenced assembly 'Microsoft.Testing.Platform' with identity 'Microsoft.Testing.Platform, Version=1.8.5.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'

[Copilot]

@copilot investigate and fix the build failure:

CSC(0,0): error CS1705: (NETCORE_ENGINEERING_TELEMETRY=Build) Assembly 'xunit.v3.mtp-v1' with identity 'xunit.v3.mtp-v1, Version=3...

The build failure is because xunit.v3.mtp-v1 3.2.2 requires Microsoft.Testing.Platform 1.9.1, but the pinned Arcade SDK (11.0.0-beta.26070.3 in global.json) provides an older MicrosoftTestingPlatformVersion (1.8.5). Fixed in cbc685e by adding MicrosoftTestingPlatformVersion override to Directory.Packages.props to match the value in DefaultVersions.props.