Update .NET Version to 9.0

[Copilot]

Updates the project from .NET 8.0 to .NET 9.0.

Project Files

• Target framework updated to net9.0 in all csproj files (NetCore.Utilities, Tests, EncryptionKeyGenerator)
• Microsoft.Extensions.* packages updated from 8.0.0 → 9.0.0

CI/CD

• GitHub Actions workflows updated to use dotnet-version: 9.0.x

Note: Microsoft.SourceLink.GitHub remains at 8.0.0 (latest available, compatible with .NET 9.0).

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 to .NET 9.0 including build.</issue_description>

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

• Fixes Update .NET Version #66

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