Bump Microsoft.SemanticKernel and Microsoft.SemanticKernel.Abstractions

Bumps [Microsoft.SemanticKernel](https://github.com/microsoft/semantic-kernel) and [Microsoft.SemanticKernel.Abstractions](https://github.com/microsoft/semantic-kernel). These dependencies needed to be updated together.

Updates `Microsoft.SemanticKernel` from 1.15.1 to 1.28.0
- [Release notes](https://github.com/microsoft/semantic-kernel/releases)
- [Commits](microsoft/semantic-kernel@dotnet-1.15.1...dotnet-1.28.0)

Updates `Microsoft.SemanticKernel.Abstractions` from 1.15.1 to 1.28.0
- [Release notes](https://github.com/microsoft/semantic-kernel/releases)
- [Commits](microsoft/semantic-kernel@dotnet-1.15.1...dotnet-1.28.0)

---
updated-dependencies:
- dependency-name: Microsoft.SemanticKernel
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: Microsoft.SemanticKernel.Abstractions
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

webapi/CopilotChatWebApi.csproj

@@ -24,8 +24,8 @@
     <PackageReference Include="Microsoft.Azure.Cosmos" Version="3.44.0" />
     <PackageReference Include="Microsoft.Identity.Web" Version="2.20.0" />
     <PackageReference Include="Microsoft.KernelMemory.Abstractions" Version="0.66.240709.1" />
-    <PackageReference Include="Microsoft.SemanticKernel" Version="1.15.1" />
-    <PackageReference Include="Microsoft.SemanticKernel.Abstractions" Version="1.15.1" />
+    <PackageReference Include="Microsoft.SemanticKernel" Version="1.28.0" />
+    <PackageReference Include="Microsoft.SemanticKernel.Abstractions" Version="1.28.0" />
     <PackageReference Include="Microsoft.SemanticKernel.Connectors.AzureAISearch" Version="1.5.0-alpha" />
     <PackageReference Include="Microsoft.SemanticKernel.Connectors.Qdrant" Version="1.5.0-alpha" />
     <PackageReference Include="Microsoft.SemanticKernel.Plugins.Core" Version="1.5.0-alpha" />