ci: try to use github setup-dotnet action

.gitea/workflows/server.yaml

@@ -4,11 +4,10 @@ on: [ push ]
 
 jobs:
   build-server:
-    container: mcr.microsoft.com/dotnet/sdk:latest
     steps:
     - uses: actions/checkout@v3
+    - name: Setup dotnet
+      uses: https://github.com/actions/setup-dotnet@v3
       with:
-          fetch-depth: 0
-    commands:
-      - dotnet restore --packages
-      - dotnet build --no-restore
+        global-json-file: global.json
+    - run: dotnet build Server