.NET: Fix typo: sesionElement -> sessionElement

[Hao Xiong (XiongHaoTrigger)]

Motivation and Context

While studying the example of this framework, I discovered an error in the variable naming.

Description

Corrected the spelling error sesionElement → sessionElement in agent-framework/dotnet/samples/01-get-started/04_memory/Program.cs. This is a non-functional change that only fixes the variable name.

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.

[Copilot]

Pull request overview

This pull request corrects a spelling typo in the .NET “memory” getting-started sample by renaming sesionElement to sessionElement, improving readability without changing runtime behavior.

Changes:

• Renamed the local JsonElement variable holding serialized session state from sesionElement to sessionElement.
• Updated the corresponding deserialization call to use the corrected variable name.