Merged PR 49313: Fix droppped MSBuild internal feed for the 17.8 fix

Fix droppped MSBuild internal feed for the 17.8 fix

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#### AI description  (iteration 1)
#### PR Classification
Bug fix

#### PR Summary
This pull request fixes the dropped MSBuild internal feed for version 17.8.
- `NuGet.config`: Added the missing internal feed `darc-int-DotNet-msbuild-Trusted-3ab07f0` to the package sources and enabled it.
<!-- GitOpsUserAgent=GitOps.Apps.Server.pullrequestcopilot -->

Author: rainersigwald

NuGet.config

@@ -13,6 +13,7 @@
     <add key="darc-int-dotnet-aspnetcore-4ae1269" value="https://pkgs.dev.azure.com/dnceng/internal/_packaging/darc-int-dotnet-aspnetcore-4ae1269b/nuget/v3/index.json" />
     <!--  End: Package sources from dotnet-aspnetcore -->
     <!--  Begin: Package sources from DotNet-msbuild-Trusted -->
+    <add key="darc-int-DotNet-msbuild-Trusted-3ab07f0" value="https://pkgs.dev.azure.com/dnceng/internal/_packaging/darc-int-DotNet-msbuild-Trusted-3ab07f0c/nuget/v3/index.json" />
     <add key="darc-int-DotNet-msbuild-Trusted-933b72e" value="https://pkgs.dev.azure.com/dnceng/internal/_packaging/darc-int-DotNet-msbuild-Trusted-933b72e3/nuget/v3/index.json" />
     <!--  End: Package sources from DotNet-msbuild-Trusted -->
     <!--  Begin: Package sources from dotnet-roslyn-analyzers -->
@@ -53,6 +54,7 @@
     <!--  Begin: Package sources from dotnet-aspnetcore -->
     <add key="darc-int-dotnet-aspnetcore-4ae1269" value="true" />
     <!--  Begin: Package sources from DotNet-msbuild-Trusted -->
+    <add key="darc-int-DotNet-msbuild-Trusted-3ab07f0" value="true" />
     <add key="darc-int-DotNet-msbuild-Trusted-933b72e" value="true" />
     <!--  End: Package sources from DotNet-msbuild-Trusted -->
     <!--  Begin: Package sources from dotnet-format -->