.Net: Use preview suffix for Agents abstractions (#10745)

### Motivation and Context

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### Description

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### Contribution Checklist

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- [ ] The code builds clean without any errors or warnings
- [ ] 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
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone 😄

dotnet/nuget/nuget-package.props

@@ -1,15 +1,15 @@
 <Project>
   <PropertyGroup>
     <!-- Central version prefix - applies to all nuget packages. -->
-    <VersionPrefix>1.40.0</VersionPrefix>
+    <VersionPrefix>1.40.1</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>1.39.0</PackageValidationBaselineVersion>
+    <PackageValidationBaselineVersion>1.40.0</PackageValidationBaselineVersion>
     <!-- Validate assembly attributes only for Publish builds -->
     <NoWarn Condition="'$(Configuration)' != 'Publish'">$(NoWarn);CP0003</NoWarn>
     <!-- Do not validate reference assemblies -->

dotnet/src/Agents/Abstractions/Agents.Abstractions.csproj

@@ -6,7 +6,7 @@
     <RootNamespace>Microsoft.SemanticKernel.Agents</RootNamespace>
     <TargetFrameworks>net8.0;netstandard2.0</TargetFrameworks>
     <EnablePackageValidation>false</EnablePackageValidation>
-    <VersionSuffix>rc</VersionSuffix>
+    <VersionSuffix>preview</VersionSuffix>
   </PropertyGroup>
 
   <Import Project="$(RepoRoot)/dotnet/nuget/nuget-package.props" />