ruby-3.0.3のpathnameも0.1.0のようですねー
$ ls -d ~/.rbenv/versions/3.0.[23]/lib/ruby/gems/3.0.0/gems/pathname-*
/home/zunda/.rbenv/versions/3.0.2/lib/ruby/gems/3.0.0/gems/pathname-0.1.0
/home/zunda/.rbenv/versions/3.0.3/lib/ruby/gems/3.0.0/gems/pathname-0.1.0