Hardcode NuGet trusted publishing user (#3266)

Use the public nuget.org publisher identifier directly so trusted publishing does not depend on an environment-scoped secret.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: jfversluis

.github/workflows/dotnet-build.yml

@@ -405,7 +405,7 @@ jobs:
                 id: login
                 uses: NuGet/login@8d196754b4036150537f80ac539e15c2f1028841 # v1
                 with:
-                    user: ${{ secrets.NUGET_USER }}
+                    user: jfversluis_MSFT
 
             -   name: Push to NuGet.org
                 run: >