The odd thing is that SourceForge has (sf.net) a GitHub project importer (for more than 10 years now!), but not vice versa. You can import a SVN repository in GitHub, but that’s far from importing a complete sf.net project.
More on the importer to import GitHub to SourceForge below, but first the other way around:
These steps worked to get xn-resource-editor.sf.net into github.com/jpluimers/XN-Resource-Editor-TWM (which I did because the GitHub web UI is so much better at browsing and searching commits and files than the SourceForge web UI):





