fix: Fix release.yml workflow failures on ubuntu-latest

[Blackhex]

Fixes failures of https://github.com/a2aproject/a2a-dotnet/blob/main/.github/workflows/release.yaml workflow on ubuntu-latest (e.g. https://github.com/a2aproject/a2a-dotnet/actions/runs/16985047713) by installing 8.0.x version of .NET (together with the 9.0.x version) using actions/setup-dotnet action.

Validated by https://github.com/Blackhex/a2a-dotnet/actions/runs/16988888966.

[gemini-code-assist]

Note

Gemini is unable to generate a summary for this pull request due to the file types involved not being currently supported.

[Copilot]

Pull Request Overview

This PR fixes the release.yml workflow failures on ubuntu-latest by installing both .NET 8.0.x and 9.0.x versions instead of only 9.0.x. This ensures compatibility with projects that may require .NET 8.0.x while maintaining support for .NET 9.0.x.

Key changes:

• Modified the dotnet-version configuration to install multiple .NET versions using YAML multi-line syntax

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.
You can also share your feedback on Copilot code review for a chance to win a $100 gift card. Take the survey.}