fix(ci): make push step idempotent (#1062)

Author: fgreinacher

.github/workflows/ci.yml

@@ -108,7 +108,7 @@ jobs:
           name: NuGet packages
           path: packages
       - name: Push packages
-        run: dotnet nuget push "packages/*.nupkg" --api-key ${{ secrets.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json
+        run: dotnet nuget push "packages/*.nupkg" --api-key ${{ secrets.NUGET_API_KEY }} --source https://api.nuget.org/v3/index.json --skip-duplicate
       - uses: dotnet/[email protected]
         id: nbgv
       - name: Create GitHub release