This looks as if the Tuanjie Package Manager does not work like the normal Unity 6 package manager and perhaps has a bug in downloading a package via git URL. Which exact git URL did you use?
If it continues to fail, you can either directly clone the spine-unity runtimes repository from github (see here) and then import the packages from the local package now located on your harddisk.
Alternatively you could also resort to installing via unitypackage from the download page:
https://esotericsoftware.com/spine-unity-download
