C#: implement trusted publishing.

Author: tasn

.github/workflows/csharp-release.yml

@@ -9,6 +9,8 @@ jobs:
     name: C# Release
     runs-on: ubuntu-24.04
     environment: release
+    permissions:
+      id-token: write
 
     steps:
       - uses: actions/checkout@v6
@@ -28,11 +30,17 @@ jobs:
           cd csharp
           dotnet build --configuration Release Svix --no-restore
 
+      - name: NuGet login
+        uses: NuGet/login@v1
+        id: login
+        with:
+          user: ${{ secrets.NUGET_USER }}
+
       - name: Release
         run: |
           cd csharp
           dotnet nuget push "$(find Svix/bin/Release/Svix.*.nupkg)" \
             --api-key "$NUGET_API_KEY" \
             --source "https://api.nuget.org/v3/index.json"
         env:
-          NUGET_API_KEY: ${{ secrets.NUGET_API_KEY }}
+          NUGET_API_KEY: ${{ steps.login.outputs.NUGET_API_KEY }}