Update .NET version from 8 to 9

[Copilot]

Upgrades the solution from .NET 8 to .NET 9.

Project Changes

• Target framework net8.0 → net9.0 across all projects

Package Updates

• Microsoft.Extensions.DependencyInjection: 6.0.0 → 9.0.0
• Microsoft.SourceLink.GitHub: 1.1.1 → 8.0.0
• coverlet.collector: 3.2.0 → 6.0.4
• Microsoft.NET.Test.Sdk: 17.0.0 → 17.12.0
• Moq: 4.16.1 → 4.20.72
• xunit: 2.4.1 → 2.9.3
• xunit.runner.visualstudio: 2.4.3 → 3.0.2

CI/CD

• Updated dotnet-version to 9.0.x in both workflow files
• Added explicit .NET setup step to code-quality job for consistency

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com//advisories
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (http block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update .NET Version</issue_title>
<issue_description>Update .NET version from 6 to .NET 9.</issue_description>

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

• Fixes Update .NET Version #53

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