Replace git checkout with datalad checkout in action workflows wherever appropriate

[hvgazula]

It makes much more sense and is cleaner to use datalad checkout instead of git checkout as the siblings are not readily known with the latter.

[hvgazula]

WIP datalad/datalad-action#18 (comment)

[hvgazula]

Works alright in GitHub runner but not on ec2 self-hosted runner because all actions are run as root.

[hvgazula]

changing no non-root user didn't cut either. https://github.com/neuronets/test-aws/actions/runs/7904098846

[hvgazula]

I am giving up. Thanks.

[satra]

why not just log into an ec2 instance and carry out the steps manually?

[hvgazula]

Nah..I am testing the action itself not simulating the steps in the action...