Currently, GitHub does not provide any build-in methods to clean everything in the _work directory after the job completed.
If you want to clean the _work directory, you can try to setup a step at the end of the job to use the remove command, such as rm (bash) or Remove-Item (PowerShell), to remove files in the _work directory.
- name: Clean working directory
rm -r *
However, use the commands can’t completely remove the GITHUB_WORKSPACE (_work/repos/repos) in the _work directory. The files and subfolders in GITHUB_WORKSPACE can be removed, but the folder “_work/repos/repos” will be retained and you will get the error like as “cannot remove ‘repos/repos’: Device or resource busy”.