Might be worthwhile trying without the ".git" at the end of the URL. It looks to me that the SVN URL is
https://github.com/fpc/Lazarus
See -
curl -i -u $GH_USER https://api.github.com/repos/fpc/Lazarus
......
"clone_url": "https://github.com/fpc/Lazarus.git",
"svn_url": "https://github.com/fpc/Lazarus",
.....
Davo