CI: Bump dotnet

Author: CallumDev

.github/workflows/dotnet.yml

@@ -16,7 +16,9 @@ jobs:
     - name: Setup .NET
       uses: actions/setup-dotnet@v2
       with:
-        dotnet-version: 6.0.x
+        dotnet-version: |
+          6.0.x
+          8.0.x
     - name: Restore dependencies
       working-directory: ./src
       run: dotnet restore