Update CI to net9

Author: cyanfish

.github/workflows/dotnetcore.yml

@@ -9,11 +9,11 @@ jobs:
       matrix:
         os: [windows-2022, ubuntu-24.04, macos-14]
     steps:
-    - uses: actions/checkout@v2
-    - name: Setup .NET 8
-      uses: actions/setup-dotnet@v3
+    - uses: actions/checkout@v4
+    - name: Setup .NET 9
+      uses: actions/setup-dotnet@v4
       with:
-        dotnet-version: 8.0.x
+        dotnet-version: 9.0.x
     - name: Install dependencies
       run: dotnet restore
     - name: Build