Add GitHub Actions workflow for Update Dependencies Tests with TRX artifact upload

[Copilot]

Fixes #6669

This PR adds a new GitHub Actions workflow to run the UpdateDependencies.Tests in PR validation, as requested in the issue.

What's Added

A new workflow .github/workflows/update-dependencies-tests.yml that:

• Triggers automatically on pull requests that modify:

  • eng/update-dependencies/** (the update-dependencies tool)
  • tests/UpdateDependencies.Tests/** (the test project)
  • The workflow file itself

• Runs focused tests using standard .NET commands:

  • dotnet restore to get dependencies
  • dotnet build to compile the test project
  • dotnet test to execute only the UpdateDependencies.Tests (no other repo tests)

• Publishes test results with TRX artifact upload:

  • Generates TRX test result files using --logger trx
  • Uploads TRX files as artifacts for download using actions/upload-artifact@v4

• Uses minimal resources with ubuntu-latest runner and .NET 9.0.x setup via actions/setup-dotnet@v4

Why This Approach

Following the discussion in the issue comments, this uses GitHub Actions (not Azure Pipelines) since:

• The scope is small and focused
• No need to run during unofficial builds
• Matches the pattern used in dotnet-buildtools-prereqs-docker
• Provides fast feedback for changes to the update-dependencies tool

The workflow follows the same security and formatting patterns as existing workflows in the repository, using only GitHub-created actions with minimal permissions and proper YAML structure.

This ensures that any changes to the update-dependencies tool or its tests are automatically validated in PRs with TRX test results available as downloadable artifacts, improving code quality and catching issues early.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update dependencies tests should run in PR validation</issue_title>
<issue_description>#6668 added a new test project for the eng/update-dependencies tool. It lives in tests/UpdateDependencies.Tests. Those tests should run in PR validation.

Spec:

• There should be a new GitHub action/workflow called "Update Dependencies Tests"
• It should trigger whenever a pull request is created that modifies any of the following files:
  • eng/update-dependencies/*
  • tests/UpdateDependencies.Tests/*
  • The workflow file itself
• The workflow should install .NET and run dotnet test on the UpdateDependencies.Tests project only.
• The workflow shouldn't run any other tests in the repo.</issue_description>

Comments on the Issue (you are @copilot in this section)

@lbussell @MichaelSimons @mthalman what are your opinions on GH Actions vs. Azure pipelines for this? I lean towards Actions, [similar to dotnet-buildtools-prereqs-docker](https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/main/.github/workflows/run-tests.yml). The scope is small and there is no point running these tests during unofficial builds as it won't affect the outcome. @lbussell Closely related: https://github.com//issues/6478 @MichaelSimons I don't see any issues w/this approach.

Fixes #6687

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[Copilot]

Pull Request Overview

This PR adds a GitHub Actions workflow to automatically run UpdateDependencies.Tests in PR validation, as requested in issue #6669. The workflow ensures that changes to the update-dependencies tool are properly tested during pull request validation.

• Adds a new GitHub Actions workflow that triggers on relevant file changes
• Implements focused testing using standard .NET commands (restore, build, test)
• Uses minimal resources with ubuntu-latest runner and .NET 9.0.x setup