Fix duplicate NuGet package submission in Azure Pipeline

[Copilot]

The Azure Pipeline was attempting to push NuGet packages twice, causing a 409 Conflict error during deployment. The issue occurred because the pipeline was explicitly pushing both .nupkg and .snupkg files, but NuGet automatically handles symbols packages when pushing the main package.

Problem

The pipeline configuration in azure-pipelines.yml included both patterns:

packagesToPush: '$(Build.ArtifactStagingDirectory)/packages/**/*.nupkg;$(Build.ArtifactStagingDirectory)/packages/**/*.snupkg'

This caused the following sequence:

1. Push Xunit.Microsoft.DependencyInjection.9.2.0.nupkg ✅
2. NuGet automatically pushes corresponding Xunit.Microsoft.DependencyInjection.9.2.0.snupkg ✅
3. Pipeline explicitly tries to push Xunit.Microsoft.DependencyInjection.9.2.0.snupkg again ❌
4. Results in 409 Conflict: "It looks like there is another copy of this symbols package pending validation(s)"

Solution

Updated the pipeline to only push .nupkg files and let NuGet handle the symbols packages automatically:

packagesToPush: '$(Build.ArtifactStagingDirectory)/packages/**/*.nupkg'

This eliminates the duplicate push while maintaining all existing functionality. Both the main package and symbols package are still published correctly to NuGet.org.

Fixes #324.

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