.Net: Update Microsoft.SemanticKernel packages from 1.68.0 to 1.70.0 (#13524)

### Motivation and Context

Updates Semantic Kernel package references to align with the latest
1.70.0 release.

### Description

Updated three package versions in `dotnet/Directory.Packages.props`:

- `Microsoft.SemanticKernel.Abstractions`: 1.68.0 → 1.70.0
- `Microsoft.SemanticKernel.Connectors.OpenAI`: 1.68.0 → 1.70.0
- `Microsoft.SemanticKernel.Core`: 1.68.0 → 1.70.0

### Contribution Checklist

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>Update the Microsoft.SemanticKernel packages from 1.68.0
to 1.70.0</issue_title>
> <issue_description>In this file
`https://github.com/microsoft/semantic-kernel/blob/main/dotnet/Directory.Packages.props`
> 
> Update the Microsoft.SemanticKernel packages from 1.68.0 to 1.70.0
> </issue_description>
> 
> <agent_instructions>Update the Microsoft.SemanticKernel packages from
1.68.0 to 1.70.0</agent_instructions>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



<!-- START COPILOT CODING AGENT SUFFIX -->

- Fixes #13523

<!-- START COPILOT CODING AGENT TIPS -->
---

💡 You can make Copilot smarter by setting up custom instructions,
customizing its development environment and configuring Model Context
Protocol (MCP) servers. Learn more [Copilot coding agent
tips](https://gh.io/copilot-coding-agent-tips) in the docs.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: markwallace-microsoft <127216156+markwallace-microsoft@users.noreply.github.com>

Author: Copilot

dotnet/Directory.Packages.props

@@ -80,9 +80,9 @@
     <PackageVersion Include="Microsoft.ML.OnnxRuntime" Version="1.23.2" />
     <PackageVersion Include="Microsoft.ML.OnnxRuntime.Gpu" Version="1.23.2" />
     <PackageVersion Include="Microsoft.ML.Tokenizers.Data.Cl100kBase" Version="2.0.0" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Abstractions" Version="1.68.0" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.OpenAI" Version="1.68.0" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Core" Version="1.68.0" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Abstractions" Version="1.70.0" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.OpenAI" Version="1.70.0" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Core" Version="1.70.0" />
     <PackageVersion Include="Microsoft.SemanticKernel.Planners.OpenAI" Version="1.47.0-preview" />
     <PackageVersion Include="Microsoft.VisualStudio.Threading" Version="17.14.15" />
     <PackageVersion Include="Microsoft.AspNetCore.SignalR.Client" Version="10.0.2" />