Also add a test for GogsDownloaderFactory.New() to make sure
that the URL of the source repository is parsed correctly.
When the source gogs instance is hosted at a subpath like `https://git.example.com/gogs/<username>/<reponame>` the migration fails.
This PR fixes that.
Co-authored-by: hecker <tomas.hecker@gmail.com>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/3572
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: varp0n <tom@gkstn.de>
Co-committed-by: varp0n <tom@gkstn.de>
