.NET: Update Microsoft.Agents.ObjectModel packages to 2026.2.2.1

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Motivation and Context

New package versions released to NuGet.

Description

Updated three ObjectModel packages in Directory.Packages.props:

• Microsoft.Agents.ObjectModel: 2026.1.2.3 → 2026.2.2.1
• Microsoft.Agents.ObjectModel.Json: 2026.1.2.3 → 2026.2.2.1
• Microsoft.Agents.ObjectModel.PowerFx: 2026.1.2.3 → 2026.2.2.1

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>.NET: [Feature]: Update Microsoft.Agents.ObjectModel version to 2026.2.2.1</issue_title>
<issue_description>### Description

Microsoft.Agents.ObjectModel just released a new package version to nuget.org. Update the package version of these packages in Directory.Packages.props to the new version: 2026.2.2.1

Code Sample

Language/SDK

.NET</issue_description>

<agent_instructions>After updating the package version, ensure that the projects builds correctly and tests pass.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes .NET: [Feature]: Update Microsoft.Agents.ObjectModel version to 2026.2.2.1 #4002

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[Copilot]

Pull request overview

Updates the centrally-managed .NET package versions for Microsoft.Agents.ObjectModel dependencies to the latest NuGet release, keeping the Workflows/declarative components aligned with the current ObjectModel packages.

Changes:

• Bumped Microsoft.Agents.ObjectModel, .Json, and .PowerFx from 2026.1.2.3 to 2026.2.2.1 in central package management.