.NET: Bump package version to 1.79.0 (#14275)

### Motivation and Context

Prepares the .NET packages for the next minor release.

### Description

- Bumps `VersionPrefix` from `1.78.0` to `1.79.0`.
- Advances `PackageValidationBaselineVersion` from `1.77.0` to `1.78.0`.

### 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 😄

Copilot-Session: 2a1e876a-251c-403d-bc89-8e02610a19ae

Author: SergeyMenshykh

dotnet/nuget/nuget-package.props

@@ -1,15 +1,15 @@
 <Project>
   <PropertyGroup>
     <!-- Central version prefix - applies to all nuget packages. -->
-    <VersionPrefix>1.78.0</VersionPrefix>
+    <VersionPrefix>1.79.0</VersionPrefix>
     <PackageVersion Condition="'$(VersionSuffix)' != ''">$(VersionPrefix)-$(VersionSuffix)</PackageVersion>
     <PackageVersion Condition="'$(VersionSuffix)' == ''">$(VersionPrefix)</PackageVersion>
 
     <Configurations>Debug;Release;Publish</Configurations>
     <IsPackable>true</IsPackable>
 
     <!-- Package validation. Baseline Version should be the latest version available on NuGet. -->
-    <PackageValidationBaselineVersion>1.77.0</PackageValidationBaselineVersion>
+    <PackageValidationBaselineVersion>1.78.0</PackageValidationBaselineVersion>
     <!-- Validate assembly attributes only for Publish builds -->
     <NoWarn Condition="'$(Configuration)' != 'Publish'">$(NoWarn);CP0003</NoWarn>
     <!-- Do not validate reference assemblies -->