Update GitHub Actions workflow to use .NET 8.0

Co-authored-by: wannaphong <8536487+wannaphong@users.noreply.github.com>

Author: Copilot

.github/workflows/dotnetcore.yml

@@ -8,11 +8,11 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
-    - name: Setup .NET Core
-      uses: actions/setup-dotnet@v1
+    - uses: actions/checkout@v4
+    - name: Setup .NET
+      uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 3.1.101
+        dotnet-version: '8.0.x'
     - name: Install dependencies
       run: dotnet restore
     - name: Build