ci: use setup-dotnet for test workflow

[lamg]

Motivation

• The test job used a job-level .NET SDK container which can fail due to image pull/tag or environment differences, so installing the SDK explicitly on the hosted runner ensures dotnet is available when dotnet test runs.

Description

• Removed the container: image: mcr.microsoft.com/dotnet/sdk:10.0 lines and added actions/setup-dotnet@v4 with dotnet-version: 10.0.x before running dotnet test in ./src.

Testing

• Attempted to run cd src && dotnet test in this environment but the dotnet CLI is not installed so the test run could not be executed here.

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Codex Task