Upgrade actions/checkout from v3 to v4

Author: geofranzi

.github/workflows/main.yml

@@ -11,7 +11,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Install .NET SDK
         uses: actions/setup-dotnet@v3