nuget source set in nuget.config works locally but doesn't work in Github Workflows

[eventsourcer]

I have a nuget.config file created with nuget source as shown.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <packageSources>
        <clear />
        <add key="nuget" value="https://api.nuget.org/v3/index.json" />
        <add key="github" value="https://nuget.pkg.github.com/eventstorage/index.json" />
    </packageSources>
    <packageSourceCredentials>
        <github>
            <add key="Username" value="eventstorage" />
            <add key="ClearTextPassword" value="some-password" />
        </github>
    </packageSourceCredentials>
</configuration>

running dotnet nuget push "package" -k "" -s nuget works locally with either nuget or github sources.

running the same command in a GitHub workflow says that the source is invalid:

- name: nuget push
  run: dotnet nuget push *.nupkg -k ${{ secrets.NugetApiKey }} -s nuget

at the same time attempting to create the source in the workflow fails with "provided source already exists":

- name: nuget auth
  run: >
     dotnet nuget add source --username eventstorage --password ${{ secrets.NugetApikey }}
     --store-password-in-clear-text --name nuget ${{ env.nuget_url }}

why the workflow treats the command differently? what differences are there and what do I miss?

Thank you for your help.