ci: drop useless chown call

AFAIK we anyway run self-hosted runners from root due to all those
problems like [1]. No reason to include the hack into every workflow
file. If we'll going to start runners from a non-root user, it is better
to pass `--user $PROPER_UID` to all docker jobs instead, see [2]: at
least it does not require to place a boilerplate into all workflow
files.

Didn't touch perf_* jobs: don't want to dig inside this part of the
infrastructure ATM.

It reverts PR #5953.

[1]: https://github.com/actions/checkout/issues/211
[2]: https://github.com/actions/runner/issues/691