fix: generate credentials-only NuGet config for Docker build

Omit packageSources from the generated config so NuGet's config layering
keeps nuget.config as the single source of truth for feed URLs and
packageSourceMapping rules.

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

Author: BenjaminMichaelis

.github/workflows/Build-Test-And-Deploy.yml

@@ -71,11 +71,6 @@ jobs:
           cat > /tmp/nuget-auth.config << EOF
           <?xml version="1.0" encoding="utf-8"?>
           <configuration>
-            <packageSources>
-              <clear />
-              <add key="nuget" value="https://api.nuget.org/v3/index.json" />
-              <add key="EssentialCSharp" value="https://pkgs.dev.azure.com/intelliTect/_packaging/EssentialCSharp/nuget/v3/index.json" />
-            </packageSources>
             <packageSourceCredentials>
               <EssentialCSharp>
                 <add key="Username" value="docker" />