Create your own task
You cannot inject code within the task scheduler directly (if you can, please file an issue, you discovered a vulnerability, congratulation).
Create file script
For safety reason, you need to commit here, in the shell folder, a script first. If the remote git repository GIT_REPO is a Github, Gitlab, Gogs or Gitea it should be easy to add some new file with their web editor.
Pull the script
Pull the script into the application, using the “Pull” button
Find the script
The script file should now be listed when you will create or update a job.