Update Github Workflow

Author: ahmadellahib

.github/workflows/dotnet.yml

@@ -15,7 +15,7 @@ jobs:
     - name: Installing .NET
       uses: actions/setup-dotnet@v3
       with:
-        dotnet-version: 7.0.x
+        dotnet-version: 8.0.x
     - name: Restoring Packages
       run: dotnet restore src/CourseLibrary/CourseLibrary.sln
     - name: Building Solution