fatal: cannot exec '/tmp/example.com/git-ssh.sh': Permission denied
The server you're deploying to, does not allow the execution of executables within the tmp directory, which is where Capistrano uploads git-ssh.sh
Within either your specific environment config or in your global deploy.rb add the following line:
set :tmp_dir, "/home/deploy"
This sets the temporary dir Capistrano uses to the home folder of the deploy user, where it will have permission to execute. If you want, you can also create a tmp folder under the home of the deploy user, but that would require additional work to do.