Error: Invalid argument passed to dotnet test in workflow

[Hemavathi15sg]

The CI workflow fails because the test command uses an invalid argument for 'dotnet test'. The logs state:

The argument /home/runner/work/CourseApplication/CourseApplication/api/CourseRegistration.Tests/bin/Release/net8.0/CourseRegistration.Tests.dll is invalid. Please use the /help option to check the list of valid arguments.

Proposed Solution:
Update the test running step in the workflow to:

dotnet test api/CourseRegistration.Tests/CourseRegistration.Tests.csproj --configuration Release

or simply:

dotnet test api/CourseRegistration.Tests --configuration Release

This change allows the dotnet test command to build and run tests as intended, rather than running directly on the DLL, which is not a supported usage for dotnet test.

Optional: Review CS8625 warnings in the controllers and avoid passing null to non-nullable references to improve code quality.