Use vars.NUGET_USER in ci.yml (#121)

Author: phnx47-bot

.github/workflows/ci.yml

@@ -97,7 +97,7 @@ jobs:
         uses: NuGet/login@v1
         id: login
         with:
-          user: phnx47
+          user: ${{ vars.NUGET_USER }}
       - name: Push to nuget.org
         run: |
           dotnet nuget push "*.nupkg" \