Update tests.yaml to use dotnet 8 · cooolbros/hud-merger@310f8ed

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, actions/setup-dotnet@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

Possible null reference assignment.

Unboxing a possibly null value.

Non-nullable field 'MethodsStructure' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Non-nullable event 'OnUserAchievementUpdate' must contain a non-null value when exiting constructor. Consider declaring the event as nullable.

Converting null literal or possible null value to non-nullable type.

Dereference of a possibly null reference.